|Taboo: saves any number of tabs in a local database so that it is possible to return to them later; helps to avoid keeping too many open tabs for the same purpose|
Tab To Window: Open a tab in a new window.
Not really extremely useful, but in principle a logical option to have
Tabs Open Relative. Makes all new tabs open to the right of the current tab, rather than at the far right of the tab bar.
Simple and useful. Note that it also changes behavior of "Control-T" (which is somewhat questionable IMHO).
|Stylish: Customize styles of web pages you visit often|
Adblock Plus: No comment necessary ;) Firefox being as good as it is, this is still THE major reason I am using Firefox.
One more interesting piece of history, an (indirect) dispute between known blogger Jack Lewis and Adblock Plus and his author (Wladmir Palant). More on this and issues regarding legality of Adblock Plus: [1 | 2 | 3]
|Dictionary Switcher: Rather trivial but nevertheless useful extension that helps to select correct language for spell check, and remembers choices made previously|
Fission: combines address bar and progress bar (Safari style).
This is not perhaps terribly useful in and of itself, but quickly becomes indispensable as number of other extensions grows and status bar quickly fills up with information.
Organize Status Bar: enables you to organize your status bar icons/info; rearrange and/or hide.
This could be useful after Firefox update since these status bar "items" usually come up in a different (perhaps random) order after an upgrade. Also, you can free up space by hiding some items without actually disabling corresponding extensions
|DragDropUpload: makes it much easier to select file to "upload" by using drag-n-drop UI|
FireStox: stock monitor with "advanced features"
Unfortunately, not yet upgraded to Forefox 3. Also, has some quirks like requires users to configure it only through a special site with its own registration, etc. Still, it ws useful while it was working
|StockTicker: more straightforward approach to "stock monitor". However, more often than not fails to update - obviously in need for some maintenance|
Multiple Tab Handler: Allows user to select multiple tabs and then perform certain operations on selected tabs
This was initially a project to implement some upcoming Firefox 2 features as Firefox 1.5 extension; it is now Firefox 3 but I guess not all features are yet available; most useful is "duplicate" tab, though it might be available from other extensions as well.
Open link in...: makes it possible to open links and images in a new "background" tab, in a new background or foreground window, and in the current tab.
Rarely needed in fact, but why not...
Poster: "A developer tool for interacting with web services and other web resources that lets you make HTTP requests"
So this is debugging tool, in essence. I haven't used it much yet.
IE View: Lets you load pages in IE.
This extension makes it possible to survive with Firefox as the "default browser" and still work with IE-centric applications. Simple, but useful.
GMarks: presents Google bookmarks in a spacial menu similar to "old style" pre-"Places" bookmarks
Makes Firefox 3 "places" (bookmarks replacement) almost completely irrelevant. A brilliant extension, indeed. See also this review.
Gmail Notifier: notifies you (visually and with configurable sound) about new e-mail in your g-mail Inbox
Similar functionality exists in Google Toolbar, but it makes very infrequent updates and there is no obvious way to customize that; also in gtalk, but you have to "touch" your computer in order for it to change its icon.
Forecastfox l10n: Get international weather forecasts from Weather.com
One of the many extensions that exist for weather display; not sure how it compares with others, but it works for me.
Flagfox: Displays a country flag in the status bar depicting the location of the current website's server
More for fun than for anything serious, but again, why not.
Google Notebook: Direct access to Google Notebook while browsing
One of only two Google extensions for Firefox still officially supported; useful to take notes which get instantly auto-saved on Google servers
Google Toolbar: Well, it is what is is: google toolbar.
In fact, Firefox versions lags substantially bhind latest version for IE and is lacking many useful features. However, its "autofill" feature is what I use fairly often, and also quick buttons to search for quesry words in search results; some might need spell-checking and bookmarks, though these features are reasonable well covered by GMarks (see abov) and built-in Firefox spell-checker
Google Reader Watcher: Checks your Google Reader for unread news
This sounds like a good idea, but in fact it is of limited usability, especially if you have some high-volume feeds in your subscriptions list whicj you only check occasionally; notifiers constantly shows "1000+" messages, and that's pretty much it.
|Hebrew Calendar: Show the Hebrew date in your browser's status.|
LiveJournal Addons: Provides very extensive integration between Firefox and LiveJournal engine.
Not all options are equally useful, but still, this is all but indispensable when speding time in LiveJournal. Check also http://ljaddons.livejournal.com/
Locationbar²: Shows "real" URL if there are some "urlencode"d characters in the location bar; provides some other visual enhancements
Extremely useful if e.g. you often need to browse Wikipedia or similar resource in a language based on non-latin character set
Weave: A replacement for Google browser sync, is intended to synchronize user's bookmarks and other info across multiple computers
(One of the extensions from Mozilla Labs)
This is a very early "alpha" version, and after playing with it for a while I have disabled it for now. For one thing, it does not work in my 64-bit Ubuntu (or at least not without some tweaking), and then it constantly complains that server is busy when trying to synchronize. Finally, I am really using GMarks in place of Firefox bookmarks, which are already synchronized; thus I do not gain much from this extension anyway.
Snowl: powerful built-in feed reader
Also from Mozilla Labs, this is still a very early prototype; after getting used to Google Reader, it is unlikely I would want to switch to some local client. Nevertheless, it is worth following up in a while.
Dictionary Tooltip: Brings dictionary lookup results in instantaneous pop-up frame
It is only in this list for historical reason, I am not recommending installing it. First, developer is apparently asking for money (albeit not a lot) in order to get the latest version. Then, many users complain about poor support of Firefox 3. Finally, to translate a word while browsing I am using Lingvo, so not much else is needed.
(Some users recommend using Dictionary Lookup instead; perhaps, this is worth checking)
Sage: lightweight RSS/Atom reader.
I was using this extension for a while quite successfully along with Google browser sync to synchronize feed list; unfortunately, this combination never worked reliably, so finally I gave up and switched to Google Reader. I never tried Sage with Firefox 3 (though it is officially compatible), but I just noticed that there is now a fork Sage-Too "with lots of additional functionality and bug fixes". So, I don't know....
Abduction!: Formerly known as "Save As Image", this is a quick way to take a snapshot of a Web page.
Didn't work too well for me wheni tried it a while ago; perhaps it has improved since
User Agent Switcher: lie to a site about browser you're using
Well, it is one of the oldest and simplest Firefox extension. If you need, install it; if not, then not.
Web Developer: Adds a menu and a toolbar with various web developer tools.
Special toolbar with lots of tools, which I never really tried.
Dictionary Search: Very basic tool that allows submission of selected word to any search engine
Really simple and multi-purpose tool for quck search, translation, etc.
|Deepest Sender: originally Firefox-based client for LiveJournal, which also supports posting to Blogger and WordPress|
Xinha Here!: Provides Xinha WYSIWYG content editor as Forefox extension, in effect instantly turning each Text edit box into HTML editor.
So what it means is that site administrators can no longer bother to provide built-in HTML content editor, but simply display Text Area and tell users to install Xinha Here; I figure that right after implementing such a content editor myself ;) anyway, the only deficiency I could find is lack of support for Firefox spell checker (which works fine in Xinha itself, BTW).
Never tried it myself yet, though.
Webchunks: implements Internet Explorer Webslices in Firefox
See tutorial with link to the latest version; there is a review available at Mozilla Links, and some comments from users here.