I just pimped my Firefox with some sweet add-ons.. actually some of them should be implemented in the next FF update, coz the damn IE already has them.
1. Close'n forget - closes current tab and deletes all tracks of it (cookies, history)
2. Hyperwords - this is one good thing featured in IE8 too. After selecting some words/sentence you get some options for that: translate, locate in map, blog, search etc.
3. Next Tab - opens a new tab right next to your current one and not at the end of the tabs, like default.
4. Tab Scope - when hovering mouse pointer on a tab you get a small popup with a preview of it and some options
5. Undo Closed Tabs Button - and this happens quite often for me