Its happened multiple times, Ill have a good amount of bookmarks on firefox and one time ill restart my computer or something and reopen firefox and theyll all be gone... any idea how to stop this from reoccurring?
try reinstalling firefox, if that doesn't work, try starting a new profile in firefox. http://skvnet.blogspot.com/2007/11/create-new-profile-for-firefox-web.html anything beyond that i wouldn't know how to help, you could always try another free web browser like Opera. Opera is just as good and some would say its better than firefox.
Something seems to be corrupting your bookmarks. Are you ending Firefox properly when you restart? I'd back up your bookmarks with Foxmarks. It's even useful for when you're away from your computer.