IE Tab + (FF 8+, 7, 6, 5, 4, 3.6, 3.5, SeaMonkey) Requires Restart
IE Tab + is an enhanced version of IE Tab. It supports FF 3.5 or greater, integrates IE Tab with Adblock Plus in the IE Tab engine, and synchronizes cookies between IE and Firefox. You can easily import settings from the original IE Tab into IE Tab +
No Close Other Tabs Requires Restart
Removes "Close other tabs" context menu item.
Pins a YouTube video to the page so that it is always visible while you scroll and read comments. Port of Chrome's Video Pinner extension
Shift+LeftClick XUL Requires Restart
This simple addon has only this functionality, nothing else: it opens links in a new active tab with Shift+LeftClick (left mouse button click).
Better use https://addons.mozilla.org/ru/firefox/addon/shiftleftclick-opens-links-in-/ for FireFox.