The Web Developer extension adds various web developer tools to the browser.
When you find something on the web that you want to view later, put it in Pocket. It automatically syncs to your phone, tablet or computer so you can view it at any time, even without an internet connection.
View HTTP headers of a page and while browsing.
Save an image of a web page (including Flash content) to a file. Web page screenshots may be captured interactively or from the command line. Options allow you to control the output format (PNG or JPEG), image file name, scaling, and much more.
CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
Show the IP address of the current page in the status bar. It also allows querying custom information services by IP (right click) and see location and avaiable vouchers for shopping sites. Additionally you can copy the IP address to the clipboard.
Permanently hide content from web pages using the Context Menu. Simply, click and "Remove it Permanently". Now includes previewing of items before removal, support for IFrame as well as lots of advanced features to make it easy for...
Creates a menu to access google bookmarks from any computer. Needs Google Account to use this extension.
Allows quick access to frame functions via the context menu by overriding "Reload", "View Page Source" and "View Page Info". Instead of being applied to the main window, those functions now apply to the current frame only.
Turn tabs of your choice into permanent tabs. PermaTabs can't be closed accidentally no matter what you click (even actions like "Close other tabs" will not affect them) and will stick around between sessions.