Interesting add-ons that I don't use or have not installed
Send a tab or link to another device using Firefox Sync.
Shows source comments for advanced application preferences in about:config
CSSsir is easy and handy tool which allows you to generate cross-browser code for main CSS- rules in a few clicks.
This CSS3 generator will be useful not only for web-masters and designers but also for common users.
Use Windows and Internet Explorer Favorites directly from Firefox. No need to import, export or synchronize - the same Favorites appear...
When click on the selected tab, a history menu corresponding to it will display.
Extract Text from HTML code and make the content more readable than code
Adds a Google +1 Button to your urlbar to +1 any page. More on http://www.google.com/+1/button/
Improvement User Script Manager Greasemonkey (based on version 0.922) - Configuration Functionality for User Scripts outside Profile Folder (e.g. in DropBox Folder to share scripts)
Screen Draw lets you draw or type text over the top of any page in any colour or size and then save it to png or jpeg.
Make your Firefox menu icon colorful instead of three boring lines.
Multiple Addon Deactivator (M.A.D) is an addon that can (de)activate one, many or each addon at the same time
This add-on use regex to change a text when it is copied or pasted. Useful to
- paste modified text in a form field or url in the address field
- copy in another application some text from the web, modified when put in the clipboard