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What, Firebug? It didn't break, they integrated it with the FF dev tools. So now it's built in...

Add-ons Links
Firefox, WaterFox, and Pale Moon Browsers

For security: Get add-ons only from the Mozilla.org add-on web pages.

Visit those links with Firefox. Visiting with the latest version of Pale Moon (27.8.2) shows an error: """This add-on requires a newer version of Firefox (at least version 52.0). You are using Firefox 27.9."
Pale moon add-ons

Adblock Latitude For Pale Moon browser only. Blocks display of ads. "Adblock Latitude is a direct fork of Adblock Plus made specifically for the Pale Moon browser."

BetterPrivacy Removed by the author. Deletes Local Shared Objects, LSOs. LSOs are files placed on your computer by the Adobe Systems Flash plug-in. Use of Adobe Flash allows web sites to track you, permanently even though your browser is configured to delete the files known as "Cookies" after each re-starting of your operating system.

CanvasBiocker Prevents websites from using the Javascript <canvas> API to fingerprint them.

Classic Theme Restorer Quoting 3 paragraphs:

"This add-on will stop working when Firefox 57 arrives in November 2017."

"This add-on will stop working when Firefox 57 arrives in November 2017 and Mozilla drops support for XUL / XPCOM / legacy add-ons. It should still work on Firefox 52 ESR until ESR moves to Firefox 59 ESR in 2018 (~Q2)".

"There is no 'please port it' or 'please add support for it' this time, because the entire add-on eco system changes and the technology behind this kind of add-on gets dropped without replacement."

Cookies Manager+

Disconnect Updates to Pale Moon browser don't install.

Facebook Blocker Prevents Facebook from following you everywhere there are Facebook "Like" buttons.

Firebug "Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page..." Firebug development page.

FlashStopper Stops video autoplay and shows a preview thumbnail. On Sept. 9, 2017 does not work with YouTube because it prevents reading comments; there is a working version in the development branch.

Ghostery I don't know if Ghostery still sells data: Ghostery sells data it collects. (Business Insider, Jun 18, 2013) Ghostery web site. See the article, Ghostery is Acquired by Cliqz! (Feb 15, 2017)

HTTPS Everywhere Doesn't install in Pale Moon. Encrypts traffic by using HTTPS encryption rather than HTTP wherever web sites accept HTTPS. See How to Protect You

Perhaps if open source developers learned from these mistakes

What mistakes? Firebug has been merged into Firefox Developer Tools. This happened a long time ago.

because the plugin firebug

Firebug was integrated with the built-in Firefox developer tools. As the Firebug team says, "The Firebug extension isn't being developed or maintained any longer". Here's a migration guide.

because the plugin firebug

Firebug was integrated with the built-in Firefox developer tools. As the Firebug team says, "The Firebug extension isn't being developed or maintained any longer". Here's a migration guide.

Since Firefox has started their crazy version numbering, I've given up on upgrading. I use 27 different addons and perfectly configured to make my web browser do what I want. It is near impossible to do an upgrade without spending hours reconfiguring the addons, some of which need to be manually downloaded and have their "MaxVersion" incremented so they will install. Maybe in 6 more months when we reach Firefox 50 I'll give it a try, but until then. Firefox 8 all the way!

Application: Firefox 8.0 (20111104165243)
Total number of items: 27

- Active Stop Button 1.4.10
https://addons.mozilla.org/firefox/addon/active-stop-button/
- Adblock Plus 1.3.10
http://adblockplus.org/en/
- BetterPrivacy 1.68
http://nc.ddns.us/extensions.html
- ColorfulTabs 7.1
http://www.binaryturf.com/free-software/colorfultabs-for-firefox/
- Cookie Monster 1.1.0
https://addons.mozilla.org/en-US/firefox/addon/cookie-monster/?src=api
- Copy Link Name 1.3.2
http://www.captaincaveman.nl/
- Download Statusbar 0.9.10
http://downloadstatusbarapp.com/
- DownloadHelper 4.9.14
http://www.downloadhelper.net/
- DownThemAll! 2.0.8
http://downthemall.net/
- Export Cookies 1.2
https://addons.mozilla.org/en-US/firefox/addon/export-cookies/?src=api
- Find Toolbar Tweaks 3.0.0
http://homepage3.nifty.com/georgei/extension/ftt_en.html
- Firebug 1.8.4
http://www.getfirebug.com/
- Greasemonkey 0.9.13
http://www.greasespot.net/
- HeaderControlRevived 1.1
https://addons.mozilla.org/en-US/firefox/addon/headercontrolrevived/?src=api
- Hide Caption Titlebar Plus 2.4.1
https://addons.mozilla.org/firefox/addon/13505/
- Menu Editor 1.2.7
http://menueditor.mozdev.org/
- Movable Firefox Button 1.4
https://addons.mozilla.org/en-US/firefox/addon/movable-firefox-button/
- NoScript 2.1.7
http://noscript.net/
- OptimizeGoogle 0.78.2
http://www.optimizegoogle.com/
- RequestPolicy 0.5.27
http://www.requestpolicy.com/
- Screen Capture Elite 2.0.0.23
http://www.grizzlyape.com/
- Searchbastard 1.5.5
http://searchbastard.rosell.dk/
- SkipScreen 0.6.1.2

Right. Futz w/ CSS.

Firebug on Chrome? Not the same!

Look at this: http://getfirebug.com/wiki/index.php/Firebug_Extensions

In particular, this has been an indispensable:
http://firequery.binaryage.com/#faq

Firebug works fine on FF 5-12.
http://getfirebug.com/

The main developer of Firebug, who used to get paid by IBM to work on it, has left for Google to work on their tools. The new lead is a Mozilla Corporation employee.

This may or may not have additionally been affected by an internal Mozilla group writing their own developer tools that will ship by default and not as an extension.

Firefox is getting close to the day where Google stops donating ... er advertising with them to the tune of millions a year (http://techcrunch.com/2008/08/28/mozilla-extends-lucrative-deal-with-google-for-3-years/) . At the end of that, they're going to be sitting in a version hole compared to their benefactor's product which is now a direct competitor. It seems to me, FF is doing whatever is necessary to make themselves look competitive when all of their opponents a) own the browser space on their own devices, b) own an OS or two that supports that browser natively and c) can get away with it because they all have monopolies in their own spaces but which all fall under a single general computing umbrella that makes them seem less like an overall monopoly.

Mozilla is in an extremely unenviable position of looking old and outdated because of any kind of real mobile support, behind in version numbers compared to ALL other browsers (ie9? Opera 11.5? Chrome 1.5 billion?). I remember when Firefox defiantly announced that they wouldn't support the iPhone when even Opera was able to make it work. Do I use Opera on my iPhone? No. Does it remind me that Opera is still relevant in the mobile space? Yes.

Mozilla is starting to remind me of an aging child star. This version thing is just them acting out to get attention. There's no reality shows for old browsers though, so they'd better start figuring out how to ingratiate their plugin developers or their only supporters are going to start writing Chromebug (Whaaaa? http://blog.getfirebug.com/category/chromebug/) and Ubiquity (Nahhh...hey! https://github.com/cosimo/ubiquity-chrome/)

It's not too late. Firefox could still release its own tablet (http://www.tomsguide.com/us/firefox-mobile-firefox-fennecomb-android-tablet-ipad,news-11489.html) - but they're going to have to do it before the money starts running out and that's going to require community support, plugin developers and everyone that they're alienating with these most recent moves.

Firefox is really the bees knees for web development....
firebug for javascript...

http://getfirebug.com/

and the poorly named web developer plugin for css make firefox a potent tool.

http://chrispederick.com/work/web-developer/

every single time, Firebug and Greasemonkey stop working.

If you use a beta version of Firefox and want to use Firebug, the Firebug developers say you should use the beta version of Firebug. It would be nice if Firefox Beta automatically went out and fetched the beta version of Firebug instead of just saying the version you have is incompatible.

Greasemonkey is often more compatible than its authors let on. I'm using it with Firefox 8 Nightly and it's working fine, despite being marked as only compatible with Firefox 5. I bet it would work in your Firefox 6 Beta just fine.

There's also a competitor to Greasemonkey called Scriptish that is marked as compatible with Firefox 6 beta. I've heard good things about it but haven't tried switching yet.

track add-ons better and not refuse to load them just because they haven't yet been certified to work

That's the plan!

AMO-hosted extensions that use APIs that haven't changed are automatically assumed to work. So are extensions developed using the new SDK.

To do it safely for other extensions, we'll need to gather data from beta users (like you -- thanks!) to find out whether the extension still does its job, whether it causes crashes (crash-stats correlations), and whether it causes other widespread problems (telemetry correlations).

Future beta versions of Firefox will probably ask you whether you also want to beta-test extensions that might not be compatible. For now you have to set a hidden pref to do that.

Have you tried this? http://getfirebug.com/releases/lite/chrome/

There you go.

The firebug plugin for firefox does exactly what you need.

Probably the best thing Firefox has going for it now is dev tools like Firebug.

Virtually every decent browser in existence already has this functionality. Maybe not quite as good as firebug, but the idea is there. See Opera and Safari.

Probably the only thing going for Firefox are extensions(Chrome supports extensions now) and proper Adblock.

Safari supports extensions now too so that's going to take a big bite out of their mac market share. Probably the best thing Firefox has going for it now is dev tools like Firebug. I remember how nimble and fast it used to be back when it was still called Phoenix, what the hell happened ?

Also no View Source.

Can you test if firebug lite works?

Also no default home page (short of saving the URL as an icon in the iPad's home).

This is a feature, not a bug. Be glad Apple didn't pimp their apple.com site statistics... if any other vendor sold the iPad, it would put a useless default homepage that only served to pump their site stats (MSN?)... about:blank is exactly what I set on all browsers. The workaround to use a home dock icon is quite decent, I think, don't you?

Debugging JS with an alert window is a horrible experience.

http://getfirebug.com/. Then don't do it.

You're confusing a variety of unrelated things here. Javascript works fine in every browser that implements standards accordingly (that is, every browser with the exception of IE 6, 7 and 8). The language is not only consistent across browser, it's actually implementing some really interesting features such as list comprehension, generators, and block scoping.

And I don't know where you get the idea that debugging Javascript is any more difficult than any other scripting language. You can't claim to be a professional JS dev and not have heard of some tools.

Oh, and as a scripting language, it is one of the fastest dynamically typed languages available, in the same league as SmallTalk and Lua. The fact that Palm developers obviously used the wrong tool for the wrong job does not in any way detract from the qualities of the language.

Methinks there's a lot of people that talk crap about Javascript but have never bothered to get the proper documentation and tools. Newsflash for everyone: anyone who does professional Python and Ruby development uses debuggers and text editors specifically for that job. Just because JS runs on the browser doesn't mean it doesn't need the same level of attention.

Aza Raskin, Mozilla head of user experience and the one who is spearheading Jetpack, has stated (one link deep from TFA) ""The question we asked ourselves is what [would happen] if any eighth-grader that can write a Web page [could] fundamentally enhance the functionality of the browser"", and TFA states a "goal of allowing anyone who can build a Web site to participate in making the Web a better place to work, communicate and play".

The majority of people don't know HTML, let alone CSS, and then add to that a JavaScript requirement. Now that we have established a population base, of the people who know HTML, CSS, and JavaScript, how many are using Firefox? Who in their right mind would want to do anything complicated in JavaScript without firebug (and its associated FirePHP for PHP AJAX developers), as well as extensions such as Web Developer, DOM Inspector, Live HTTP Headers, etc...

If one defines the new breed of "major web surfers" as Web 2.0 Mashup creators, it should be apparent that this new breed of "major web surfer" would refuse to be crippled by Internet Explorer. Its only if you retain the old skool view of couch potato surfing content consumer that IE market share dominates.

Disclaimer: I hold these truths to be self-evident, but only time will tell.

I smell bullshit.

How on earth would IE 8, a browser with a UI not written in XUL, be able to "flawlessly" use a Firefox plugin like Tab Mix Plus? Unless IE 8.1 embeds all of Gecko, plus XUL, XPCom, the XPI to install the plugins, you couldn't install or run a plugin on it. And why on earth would Microsoft suddenly give in and embed other rendering engines? That's not something the dominant browser does, that's something that a low-share browser does to help with compatibility, ala Netscape 7.

I don't buy it. Furthermore, the article is light on details, has some dubious screenshots, and was published just before April Fools' Day.

P.S. If you want to use Firebug in non-Firefox browsers, then use the Lite version. It works great in IE.

I can't go through and cover your entire list, but I do know that there's an IE addin to do DOM Inspection.

Or, you could use Firebug lite.

Sure, its capabilities are pretty limited compared to real firebug, and you need to include a script in your webpage, but it can still be a great help in debugging web pages in IE.

Have you tried the web developer extension for firefox?

Dude, Firebug, Firebug and Firebug!

Not only does it allow you to modify CSS/HTML on the fly, its JavaScript debugging features are priceless. By far the BEST web development tool and the reason I'm never switching away from Firefox.

P.S.: I still have web developer because I'm still hooked on CTRL+SHIFT+A and CTRL+SHIFT+S (validate page, disable CSS respectively).

Oh, and I did not give up and use tables! And this was in the times of IE 5 and 6.

Thank Joe Pesci for FireBug!

Alternately, you can use Firebug Lite on any browser. It's not perfect, but it still works.

You clearly need to be informed about firebug lite not quite as good as the full firefox version but so much better than nothing.

Firefox gives me themes. Let's talk when Chrome offers them.

Wouldnt it be better to make it look halfway decent from the start? Then users wouldnt need to waste their time hunting down themes.

3. Web Developer Bar (nothing like this on ANY other browser)
4. FireBug (nothing like this on ANY other browser, not even Safari's inbuilt "Develop" menu options comes close for debugging)

Every major browser has an equivalent, usually nearly identical.

IE Web Developer Toolbar
Opera Web Developer Toolbar (old version, not super great)
Opera Dragonfly (new developer tools)

Plus there's always FireBug Lite.

7. Tabmix Plus

This irritates me. The default tab behavior on FireFox is terrible. I dont think anyone I know actually uses it as is.

Heck, by default Firefox wont even remember your last session (ie, what tabs you had open, etc) if it crashes. How lame is that.

You shouldnt need TabMixPlus (mind you, thats what I use too on firefox, out of need) if the tabs behaved reasonably out of the box.

9. Foxmarks which makes sure all my bookmarks (and their keyboard shortcuts) are exactly the same in my office, on my three home machines (XP, Leopard, Ubuntu)

Does anyone actually use bookmarks anymore? I just dont close the tab, and leave it running there for months or years or whatever. Or just use the auto-complete history.

I'm half joking here ... half not. I havent used bookmarks since like the early Netscape days.

Dont get me wrong, extensions in Firefox are better than NOT having them. But why cant the Mozilla folks just make Firefox better out of the box. Every time I have to build a new machine for me, or move to another, I spend 5 times as much time remembering, downloading, and configuring extensions as I do just downloading and installing firefox itself. I'd rather the product was just better in the first place, and then it wouldnt need as many extensions (and wouldnt waste so much of my time).

But with Firefox, you need plugins/extensions to do ANYTHING. The product is just not that good out of the box. But you shouldnt have to spend so much time doing that, when they could just make the product more reasonable from the start.

Until recently, the reasons to use FireFox was web app development, because of FireBug, LiveHTTP Headers, and Web Developer Toolbar. Plus it had the most consistently reliable javascript performance for non-IE targeted web apps.

But nowadays all the browsers have Firebug, webdev, and livehttp headers equivalents. And it looks like Chrome will be the new standard for testing javascript heavy web apps. And of course you use IE for the apps that need IE (Exchange OWA, tons of corporate intranet apps, sharepoint, etc).

And I use opera for my non-dev browsing (ie, slashdot, digg, theregister, serverside .com/.net, newspapers, blogs, naked ladies, etc). It doesnt crash as often, it doesnt suck memory so badly, page zooming actually works and has for years (firefox just barely got reasonable page zoome with 3), it works reasonably without a million plugins, etc.

I dont mean this to sound as anti-firefox ranty as it probably does. Firefox has its place, and I'm glad its there. But its just not a very good tool, outside of being a very extensible general tool. And its a shame, because you have something like Opera that 'just works' and is nearly flawless, not to mention lean, fast, and beautiful.

So for 'personal browsing' type of use, Opera is better, at least IMO. And for app-dev/app-use, what FireFox used to be the king of, Chrom

firebuglite

I haven't actually tried this yet, but it looks cool.

Firebug does have a BETA available for FF3.
http://getfirebug.com/releases/index.html
Get Beta 1.2, not 1.0.

I've been using it for awhile. It "works". It even has some nifty interface changes (eg. being able to disable specific parts of Firebug but not others). But it's certainly a lot less stable. The Net panel sometimes lies to you and the JavaScript debugger can break or change the behaviour of pages. So, it's not as good an experience, but it works.

(Also as I said above, you can disable bits that are misbehaving).

Is available, and has been for quite some time. You just need to click on the "releases" link on the http://www.getfirebug.com/ site. Or just go directly to the extension page: https://addons.mozilla.org/en-US/firefox/addon/1843

I find the awesome bar irritating because I'm not used to it, but I know I'll have adapted by next week. As for firebug, Google is your friend Everyone I've updated has commented on how much faster it is compared to v2.

The firebug beta (download) works with FF3. I use it almost every day with no issues.

The firebug beta (download) works with FF3. I use it almost every day with no issues.

There's a beta version of Firebug that's compatible with Firefox 3. Unfortunately it's not on the main addons site yet, and the Firebug site doesn't seem to be responding right now.

I'd suggest you check the firebug releases page. They appear to have released a version that supports firefox 3 (1.2b3 so far). Not sure how buggy it is at the moment, but from what i recall about firebug 1.0.5 under ff3, this can't be too bad.

I haven't actually tried this yet, but I got all excited when I saw it: firebug lite

Actually, for Firefox 3 you want Firebug 1.2 (not done yet).

There is a beta (1.1) on the Firebug page which works just fine in FF3.

From a user experience, I believe vanilla IE is probably about the same as vanilla Firefox. It's once you start getting into some of the many great extensions for Firefox, which IE has a handful of pitiful cones for that the experience diversifies quickly.

From a developer experience, Firefox is hands down better. It is simply easier to get pages working right the first time when you're trying to break away from 1999 era table layouts and into a modern CSS/CSS2 or XML/XSL page styling. Firefox gives meaningful javascript errors (vs IE's miserable "Object does not support this property or method, line 1234" [which is often not a line number which agrees with the script line which generates the error, even for included scripts]).

Oh so often, we create pages off the bat which look great in Firefox, Opera, Safari, and even Konqueror, fire up IE, and it looks horrible. An hour of fiddling with IE to make it work right later, and now it looks wrong in all the other browsers. Eventually of course we get it to work, but not before we took elegant, short, simple code and bastardized it to pieces. But the user's experience is the same, so the user doesn't know which browser is actually better, because we can't afford to ignore the majority browser even if it is crap.

Also, development in Firefox with these two extensions has made my life immeasurably easier: Web Developer Toolbar by Chris Pedrick, and Firebug (in which I am always managing to discover new features that have been there all along). I shudder and groan when it's time to make it work in IE, because I know that javascript debugging, or CSS debugging, or just "Operation Aborted" errors are going to keep me unproductively busy for hours.

Forget "power" ripping tools; they all seem to just come down to a regex through the source, pre-set for a given handful of sites. So, they break as soon as a site updates their page layout, and just plain don't work on other, more obscure, sites.

The best way I've found is to just open up Firebug to the 'Net' tab (looks like this), and look for the biggest request listed. This works because the browser has to make the request for the video at some point, even if that request is obfuscated in the source, occurs in Javascript, doesn't end in .flv, and so on. From there, it's just a right-click, and "Copy Location".

I believe Firebug is one of the best tools available for web performance testing. The network analisys graphs will easily show which files take longer to load. This is particularly important with big js files, that are normally loaded one at a time and never in parallel.

Take a look at it at http://www.getfirebug.com/

Reposted with formatting...

I just got modded a troll.

Please try Firebug and Opera Developer Tools and then make up your own mind.

Firebug has a cool feature that lets you click on any element on the page, which shows you its position in the DOM, the associated styles and which style sheet they came from. You can edit any part of the document or the style sheet and see the changes in real time.

In Opera Developer Tools, you have to click on each node in the DOM down to the element you want, using only the tag name and its id. This takes six to ten clicks on most documents and you're doing it blind unless you know the page structure intimately. Once you get there all the properties are read-only.

Firebug also has a full debugger for JavaScript, including the ability to set breakpoints and step thru JavaScript source code, all without making any modifications to the web site (i.e. you can do it on any site, you don't need write access to the web server). There is no equivalent feature for Opera.

Yes, I'm spoiled by Firebug, but that doesn't make me a troll.

I just got modded a troll. Please try Firebug and Opera Developer Tools and then make up your own mind. Firebug has a cool feature that lets you click on any element on the page, which shows you its position in the DOM, the associated styles and which style sheet they came from. You can edit any part of the document or the style sheet and see the changes in real time. In Opera Developer Tools, you have to click on each node in the DOM down to the element you want, using only the tag name and its id. This takes six to ten clicks on most documents and you're doing it blind unless you know the page structure intimately. Once you get there all the properties are read-only. Firebug also has a full debugger for JavaScript, including the ability to set breakpoints and step thru JavaScript source code, all without making any modifications to the web site (i.e. you can do it on any site, you don't need write access to the web server). There is no equivalent feature for Opera. Yes, I'm spoiled by Firebug, but that doesn't make me a troll.

http://www.getfirebug.com/

Firebug integrates with Firefox to put a wealth of web development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

I found a way to enable Discussions2 if you previously signed up for the Univ of Michigan testing, but it isn't straight forward.

There are two ways to do it.

1. If you are using Firefox, you can install the Firebug Addon and then go to the comments preference page and click on the firebug icon in the status bar. Then click "Inspect" Firebug button and click on the "University of Michigan Testing" button and click on the HTML tab in Firebug. Change the value from "uofm" to "slashdot". Then make sure the "University of Michigan Testing" is selected and submit the page.

2. If you can't or won't use Firebug, you can do it manually by going to the comment page and saving the page on to your computer and editing the HTML to change the "uofm" value to "slashdot" and then change the submit URL from "/users.pl" to "http://slashdot.org/users.pl". Then open this page in your browser and select the "University of Michigan Testing" style option and submit the page.

Either way, if you did it correctly, then neither option under "Discussion Style" will be checked and you will be using the new Discussion2 style. You can then use the Discussion2 style without having to wait for a fix.

I love static typing. It makes all the bad problems go away.

I suppose that maybe you were being facetious or sarcastic, or maybe you were simplifying, but static typing hardly "makes all the bad problems go away". Unfortunately, I don't remember who originally said it, so I can't properly attribute it, but, paraphrasing, "static typing is the compiler doing some cursory testing on your code". To raise your level of certainty that your programme is bug-free, you have to do a lot of testing. If you use a statically-typed language, then the compiler will do some testing for you--it'll tell you that every time you call a function, the arguments you pass are the correct type and the return value is stored in a variable of the correct type. It won't tell you whether or not your code contains a logic error. Passing the wrong object to a function is an error in the programmer's reasoning that is, arguably, akin to the traditional kind of logic error that compilers gleefully use to generate segfaults and buffer overruns. To catch these sorts of things you need unit tests and integration tests and the whole shebang.

I think, in the typical case of Javascript in the browser, the fundamental problem is the combination of incompatible implementations, the piss-poor development environment, and the apparently widespread belief that you can write Javascript code by cutting and pasting. For anyone interested in improving their Javascript development environment, I recommed the Venkman debugger (or Firebug, but I've never used it) and Selenium. Venkman (and, apparently, its heir, Firebug) provides a real, honest-to-goodness debugger that supports breakpoints, watchpoints, stack traces, etc. Selenium is a tool for running unit tests within all of the major browsers and it can be automated. (In a past life, I had a script that fired up a virtual X server, launched IE through Wine and ran tests on my app through Selenium. I plugged this into cron and had regular reports of the output emailed to me.)

Ian

...here is a list of the extensions from TFA:
StumbleUpon Yahoo! Mail Notifier Gmail Manager Greasemonkey
Firefox Showcase Cooliris Previews Colorful Tabs
Chroma Tabs Google Browser Sync Foxmarks Bookmark Synchronizer Session Manager
All-in-One Gestures IE Tab Download Statusbar Download Sort
Nuke Anything Enhanced ForecastFox Answers FireFTP
Firebug Web Developer MeasureIt
ColorZilla

Tools for taming the Web
StumbleUpon
Yahoo Mail Notifier
Gmail Manager
Greasemonkey

Visual Improvements
Firefox Showcase
Cooliris Previews
Colorful Tabs
ChromaTabs

Matters of convenience
Google Browser Sync
Foxmarks Bookmark Synchronizer
Session Manager
All-in-One Gestures
IE Tab
Download Statusbar
Download Sort
Nuke Anything Enhanced

Information gatherers
Forecastfox
Answers

Web developer essentials
FireFTP
Firebug
Web Developer
MeasureIt
ColorZilla

Yes, there are more than twenty, but 20 sounds better, doesn't it? By the way, please skip the IE tab. If you are using Firefox, it is in your best interest to abandon sites that only support Internet Explorer. I should go on to say something more, because I apparently don't have enough characters per line: more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more more