Here is an attempt to collect the 50 popular and best firefox extensions which make your browsing, downloading and navigation in Firefox as easy as possible, while harnessing the full power and features of Firefox.

These extensions should work on the latest versions of the Firefox. Use the extensions which work best for your needs. The fastest way to install these extensions from developer sites is to drag them to the url bar.

When you upgrade to a new Firefox version, some extensions might not work till the AddOn owners upgrade them, use the Nightly testers tools to remove compatibility issues.

Control Firefox Tabs

• All-in-One Gestures – merges the popular following extensions for management of mouse gestures, scrolling and power navigation. (Mix of Mouse Gestures, Rocker navigation, Tab scroller, History scroller, Link tooltip and Autoscrolling extensions)
• Tabbrowser Preferences – a comprehensive UI for changing a number of the hidden tabbed browsing preferences in Firefox. It also provides the ability to control how internal and external links are opened in the browser and how the browser will react when links are sent to it.
• Tab Mix Plus – More tweaks added to tabs. Ability to select and open muliple links in tabs, open link in a duplicated tab, merge tabs and close tabs from similar domain…
• Colorful Tabs – Colors every tab in a different color and makes them easy to distinguish while beautifying the overall appeal of the interface.
• Viamatic foXpose – Click on the icon in the status bar to view all the browser windows with a single click.
• Firefox Showcase – easily locate and select any open browser window in Firefox.
• Separe – Helps you keeping tabs tidy by introducing a new kind of tab.
• Permatabs – turn tabs of your choice into permanent tabs that can’t be closed, and stick around between sessions.
• FaviconizeTab – resizes the width of the tab to display the favicon only (and back again).
• Undo Closed Tabs – allows you to undo closed tabs via a toolbar and/or tab bar button or the right-click context menu.

Control Website Links

• Linky – Lets you open or download all or selected links, image links and even web addresses found in the text in separate or different tabs or windows.
• Linkification – Allows Firefox to view plain-text URLs and e-mail addresses as actual links
• IE Tab – can open the current page or a selected link embedding Internet Explorer in tabs of Mozilla/Firefox. Very useful for those IE only pages.
• FirefoxView – Open Firefox with the current page or a selected link displayed in Internet Explorer. Adds “View in Firefox” menu items to the content and link context menus.
• Paste and Go – lets you paste an URL from the clipboard into the address bar and load it as a single step, either via the adress bar’s context menu or by pressing Ctrl-Shift-V
• ErrorZilla – changes the default 404 error page with following choices: a google cache, an archival snapshot from the wayback machine, a ping, a trace route, and a whois lookup.
• Hyperwords – Interact with all the words on the web, not just links!

Control File Downloads

• FlashGot – handles single and massive downloads with several external Download Managers.
• PDF Download – Every time you click on a link, checks if the target is a pdf file and in this case let you choose what you want to do (open pdf file inside a new tab, download it to the filesystem or view it as HTML).
• ScrapBook – helps you to save Web pages and easily manage collections.
• DownThemAll! – adds new advanced downloading capabilities to your browser. It lets you download in just one click all the links or images contained in a webpage or refine your preferences using fully customizable filters.
• Video DownloadHelper – The easy way to download Web videos from hundreds of YouTube-like sites, audio and picture galleries.
• TargetAlert – provides visual cues for the destinations of hyperlinks in cases of pdf, doc, zip files etc.
• Download Manager Tweak – modifies the default appearance of the firefox download manager and allows it to be opened in a separate window, the sidebar, or a tab.
• Download Statusbar – is a browser extension that allows you to keep track of ongoing and completed downloads in a hide-away statusbar
• Disable Targets For Downloads – Prevents sites spawning blank windows when clicking binary downloads.
• FireFTP – is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.
• Open IT Online – allows you to open your documents and images online without the need of any software to be installed.

Control Webpage Behaviour and Navigation

• GreaseMonkey – Install user scripts and change the behavior of any web page
• Image Zoom – Right click on an image and select a zoom option from the popup menu, or, hold down the right mouse button in combination with the mouse wheel to zoom in or out on an image.
• Fasterfox – Speeds up Firefox by recycling idle bandwidth by silently prefetching and caching all of the links on the page you are browsing. (Some readers said it actually slowed down their firefox – verify yourself)
• SpellBound – enables spell checking in web forms such as html textarea / input elements (html input password elements are not checked by SpellBound) and rich text form elements. This allows you to spell check forms before submitting them.
• Taboo – lets you save a page for later (taking a screenshot, and using the Session Saver code to remember scroll location and form fields).
• BugMeNot – Bypasses compulsory web registration using the BugMeNot without the hassle of surfing to it and querying its database everytime.
• AutoCopy – Select text on any web page and it will be automatically copied to the clipboard. Middle click to Paste.
• Copy Plain Text – Copies text without formatting.
• Google Images Re-Linker – This will let you click the thumbnail images on images.google.com, skip the referred framed page, and jump straight to the full-size image.
• Extended Statusbar – adds an Opera-like statusbar for Firefox that shows number of loaded images, bytes downloaded, average download speed, load time and percentage of the page loaded.
• Adblock Plus – is an enhanced version of Adblock. Block ads, applets, flash, embedded-media etc.
• Flashblock – blocks all Flash content from loading on a webpage.
• Sage-Too – add a lightweight RSS and Atom feed aggregator which integrates with Firefox’s bookmark storage and Live Bookmarks.
• Pearl Crescent Page Saver – capture screenshots and save full webpages as images easily.
• Reload Every – adds an option to the context menu to reload the web page you are viewing every so many seconds or minutes. Useful if you keep refreshing some pages often.
• InFormEnter – adds a small, clickable icon next to every input field in a web form, from where you can select the item to be inserted with your frequently used information such as name, email, address and whatever else you want to be available from the form menu.
• All-in-One Sidebar – is a sidebar control, inspired by Opera that lets you quickly switch between sidebars, view dialog windows such as downloads, extensions, and more in the sidebar, or view source code or websites in the sidebar. Can be extensively customized.
• Text size toolbar – Adds buttons to increase or decrease text size or restore default size easily. Useful for those small unreadable font sizes.
• Reveal – allows you to see thumbnails of pages in your session history and quickly find the page you want.
• Mystickies – allows you to place sticky notes all over the web and organize them with tags.
• Clear Cache Button – Adds a clear cache toolbar button that cleans the cache in one click. Very handy for those who have use for it.
• gTranslate – translate any text in a webpage just by selecting and right-clicking over it. Uses the Google translation services.
• Xinha Here! – is a wrapper for the Xinha HTML editor that enables WYSIWYG editing in any textarea and text box on any website.
• Yoono – instantly suggests alternate sites and people who share the same interests while you are surfing.
• BlueOrganizer – It helps you personalize your web experience based on what you already like, helping you discover relevant new information and save time.
• PicLens – transforms your browser into a visually stunning experience for finding and viewing online photos and videos.
• Feed Sidebar – displays the items from your Live Bookmarks in the sidebar.

Newly Added:

• Watchmelater – allows you to watch web based video from sites like youtube, myspace, revver etc, when it suits you, rather than when you stumble accross them. You could think of it as timeshifting for online video.