The day was saved by Firefox's page cache. I typed in a reply on a forum thread, clicked "post reply" and then closed the tab, only to realize that I wasn't logged in and that a login dialog had popped up just as I had closed the tab. I right-clicked the tab-list and clicked "Undo Closed Tab" and poof!! the complete tab with all its state was there, awaiting my credentials!!
Awesome stuff Firefox... I love you!!