Most Popular Extensions
Tamper Data Requires Restart Featured
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...
Webmail Ad Blocker Featured
Expand your email area by blocking and removing ads on the right hand side of the screen when using Gmail, Hotmail, Outlook.com and Yahoo Mail.
Cookies Manager+ Requires Restart
Cookies manager to view, edit and create new cookies. It also shows extra information about cookies, allows edit multiple cookies at once and backup/restore them.
Modify Headers Requires Restart
Add, modify and filter the HTTP request headers sent to web servers. This addon is particularly useful for Mobile web development, HTTP testing and privacy.
Theme Font & Size Changer Featured
Theme Font & Size Changer lets you change the global font size and font family used for the user interface in Firefox. Design your browser with your favorite font.
Quickly toggle between blocking all pop-up windows and allowing some pop-ups
R-kiosk Requires Restart
Real Kiosk is a Firefox extension that defaults to full screen, disables all menus, toolbars, key commands and right button menus. Alt+Home still takes you home. ...
Download Manager (S3) Requires Restart
View and manage downloads from a tidy statusbar
This is a new life in Firefox 26+ for old well-known addon Download Statusbar
New Features: Replace Downloads Library page.
Now you have full control of your downloads history!
Selenium IDE Requires Restart
Selenium IDE is an integrated development environment for Selenium tests. It is implemented as a Firefox extension, and allows you to record, edit, and debug tests.
Gmail™ Notifier (restartless) Featured
Multiple account (or label) Gmail notifier (without storing passwords)
UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.
Notifier for gmail, yahoo, hotmail, aol and more webmails.
X-notifier(aka WebMail Notifier) checks your webmail accounts and notifies the number of unread emails...
Supports : gmail, yahoo, hotmail, POP3/IMAP, facebook, twitter and more
Override browser user agent string
Saved Password Editor Requires Restart Featured
Adds the ability to create and edit entries in the password manager.
WhatsApp™ Desktop provides an easy access to WhatsApp Web, and notifies you of incoming posts.
Protects your privacy by blocking spying ads and invisible trackers. Warning: This add-on is in alpha, so you may find some bugs! Read more: https://www.eff.org/privacybadger
FirePath Requires Restart
FirePath is a Firebug extension that adds a development tool to edit, inspect and generate XPath 1.0 expressions, CSS 3 selectors and JQuery selectors (Sizzle selector engine).
Lookup scholarly articles as you browse the web.
HttpRequester Requires Restart
A tool for easily making HTTP requests (GET/PUT/POST/DELETE), viewing the responses, and keeping a history of transactions.