Tab Scope is a very handy Firefox add-on that shows a pop-up preview of a tab's contents when hovering over a non-selected tab...oh, a picture probably will say it better:
The developers have clearly put a huge amount of work into Tab Scope over the years and have largely got it right, and in addition to a preview image, there's a couple of controls like back, forward, refresh in the pop-up itself. After using Tab Scope version 0.3 with the fx4 theme for a couple of weeks, there's a few things on my wish list, however:
Left-clicking on the actual preview image...