RefControl Requires Restart
Control what gets sent as the HTTP Referer on a per-site basis.
HttpFox Requires Restart
An HTTP analyzer addon for Firefox
Link Properties Plus Requires Restart
Provides extended link properties: size of linked file, last modified time, etc.
Firesizer Requires Restart
Allows you to resize the window to specific dimensions.
NOTE: Users of Firefox 29 and above must install "The Addon Bar" extension to use this, as Firesizer uses the add-on bar that has been removed in Firefox 29.
Font Finder Requires Restart
FontFinder is created for designers, developers and typographers. It allows a user to analyze the font information of any element on a page, copy any piece(s) of that information to the clipboard, and perform inline replacements to test new layouts.
Track Package Requires Restart
Track Packages from the right-click menu...
Copy Pure Text Requires Restart
Allows to copy selected text as plain text by adding a 'Copy as Text' menu item to context menu.
IE Tab + (FF 8+, 7, 6, 5, 4, 3.6, 3.5, SeaMonkey) Requires Restart
IE Tab + is an enhanced version of IE Tab. It supports FF 3.5 or greater, integrates IE Tab with Adblock Plus in the IE Tab engine, and synchronizes cookies between IE and Firefox. You can easily import settings from the original IE Tab into IE Tab +
In the DOM Inspector,quickly navigate to the any elements
Search with Joy! Block Ads While Surfing!
Console² Requires Restart
Transform the colors of entire web pages or selected elements. Combine predefined themes with basic transforms. Save transforms for specific web domains.
Scriptish Requires Restart
The greatest user script engine on the Internet (a fork of Greasemonkey).
Linky Requires Restart
Linky will increase your power to handle links. ...
Manages the Remote XUL whitelist to allow websites and local files to load XUL content. For versions compatible with Firefox 41 and lower, see All Versions page below.
Linkification Requires Restart
Converts text links into genuine, clickable links...
Colorize entire web pages. Configure themes using sliders and drag-and-drop. Set domain preferences for automatic coloration.
NoRedirect Requires Restart
NoRedirect lets the user take control of HTTP redirects. It can be used to interdict an ISP's DNS search redirection hijacks, preview/screen "shortened" URLs (e.g., TinyURL), stop the annoying redirection of "smart" error pages, etc.
Whois Lookup & Hosting & DNS & Site Flags Firefox Requires Restart
IP Whois Lookup & Website Reviews & Rating. Display country flag indicating website location. Alexa and Norton Antivirus Site Adviser. Supported: GoDaddy, NetworkSolutions, Dotster, 1and1, NameCheap, Register, Yahoo, 123-Reg, FatCow, Enom, FastHosts.
Shows source comments for advanced application preferences in about:config