http://img-url.com/u/screenshot2-1297318178.png Look at the screen shot and notice the tab switcher that spans vertically along the scroll bar.
Go to Solution.
Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems can be of help, because the feature I see at your screenshot isn't native to Firefox.
I was caused by the lasttab add-on. I disabled all of my add-ons and one by one enabled them as I restarted each time. Lasttab add-on was the culprit.