Those extensions are quite new (to me at least). I'm gonna group them in this collection till I'll find the time to test them.
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.
Use PDF Download to do whatever you like with PDF files on the Web. Regain control and eliminate browser problems, view PDFs directly in Firefox as HTML, and use the all-new Web-to-PDF toolbar to save and share Web pages as high-quality PDF files.
The most beautiful yet the simplest add-on that makes a strong colorful appeal. Colors every tab in a different color and makes them easy to distinguish while beautifying the overall appearance of the interface. For Seamonkey & Flock. An essential. F...
(former Google Dictionary and Google Translate)
In-line dictionary for any word you point to or double-click; whole page translation of any web page in another language.
Better YouTube experience. Provides 'Smart Buffer' for slow connections; auto loop; buffer preferences; quality selection; and more.
Be in control of which cross-site requests are allowed. Improve the privacy of your browsing by not letting other sites know your browsing habits. Secure yourself from Cross-Site Request Forgery (CSRF) and other attacks.
The greatest user script engine on the Internet (a fork of Greasemonkey).
Wappalyzer is a browser extension that identifies software on websites.
Clears preferences left by extensions after uninstallation
Make your bookmarks bar better. Roomy Bookmarks Toolbar can: hide bookmarks/folders name, multirow, autohide and many another features(more than 20).
Customize your bookmarks bar using one add-on.
Never lose anything you type into a web form again! Lazarus securely auto-saves all forms as you type, so after a crash, server timeout, or whatever, you can go back to the form, right click, "recover form", and breathe a sigh of relief.