I keep a lot of tabs open (~60) in any particular session - I find it's faster in this way to get back to a site. About every six months or so, I lose *all* these tabs because of Firefox's inadequate session backup system. It only saves two or three total backups, some of which are completely out of date. But the worst scenario is when (1) some site pops up a new window; (2) I mistakenly close my main window before the new window; (3) I open this new saved window once or twice by accident, causing my 60-tab session backup to be overwritten. Using a third-party session manager (I have tried all the well-known ones) can mitigate this problem, but doesn't really solve it because the re-opened sessions aren't quite in the same format as Firefox sessions and so lose information. In particular, I often lose each tab's icon as well as metadata for Tree Style Tab. Could Mozilla please consider a more robust session backup system for Firefox? All it would take (I think) is to allow the user to choose the total number of backup sessions and the frequency at which a new session is added. Thank you!