Addons that are specifically for web development activities.
The best security you can get in a web browser!
Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
Never be annoyed by a Flash animation again! Blocks Flash so it won't get in your way, but if you want to see it, just click on...
The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
FoxyProxy is an advanced proxy management tool that completely replaces Firefox's limited proxying capabilities. For a simpler tool and less advanced configuration options, please use FoxyProxy Basic.
Tab Mix Plus enhances Firefox's tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured session manager.
Displays a country flag depicting the location of the current website's server and provides a multitude of tools such as site safety checks, whois, translation, similar sites, validation, URL shortening, and more...
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...
View HTTP headers of a page and while browsing.
Adds toolbar buttons to the customize toolbar window in several programs including Firefox, Thunderbird and SeaMonkey. Some of the buttons make commonly preformed actions quicker, others add new functionality.
YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
URL Fixer fixes common typos in URLs entered in the address bar. It will fix errors like "google.con" or "youtube,com". You have the option of being asked to confirm corrections before they are applied.
Control what gets sent as the HTTP Referer on a per-site basis.
Bypass compulsory web registration with the context menu via www.bugmenot.com.
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.