My favourite Firefox tweaks

• All-In-One Gestures: execute common operations with mouse gestures. I like these bindings:
  • left/right: previous/next tab
    
  • down: close tab
    
  • up: new tab
    
  • up,left,right: undo close tab
  
  This way I can perform tab operations without having to precisely locate the tab or even to look at the tab bar. Also, when "undo close tab" is readily available you can map the (very common) "close tab" operation to an easy gesture without having to be careful with it.
  
• SessionSaver: I wish this had been available back when Firefox was more unstable. Even now, it makes trying out extensions a lot more convenient.
  
• MediaPlayer Connectivity: Play embedded video files in the player of your choice. You don't have to read the source code of the page to see the videos anymore! Yay!