In firefox check your cookies file, almost every site puts a cookie on there, so probably can figure out some of the sites from that. If you sync'ed your browser, then that information might be on another device, depending on which device is the control for the sync and if you've used the other device. If it had crashed, in your profile folder, look for a file called sessionstore, there may be several, find the one on the date or nearest the date you are looking for, it might be there. Also if it crashed, check the files in the crash folder.