I have a feeling you are using a PC but maybe the same information will apply.
On the Mac, I found bookmark data in the following directory:
Firefox > Profiles> qmai3f7g.default> bookmarkbackups
I assume that qmai3f7g.default folder is unique to me so yours will likely be different. Just look for the bookmarksbackup folder. It seems to make a file for each day you log on. So even if the one for today got hosed, you may be able to rename a previous one with the current date and trick it. Don't really know for sure.
I have no idea why. The computer locked up, I restarted, and now Firefox is completely blank.
I hate. Technology. So much.
Anyone know where Firefox stores all the config data? Maybe its still there...