"Recently Closed Windows" is even better, for those times when you accidentally manage to close your main browser window with 200 open tabs, expecting Firefox to restore them the next time you start the browser, without realizing that you have a dinky little popup window left over somewhere.
But also note that Opera's had a Recently Closed Tabs dialog for as long as I can remember.
BTW, History / Recently Closed Tabs is one of my favorite FF (only) features.