I use Firefox and like did like it. Last week it dumped ALL my book marks, *poof* all gone. Dont know the cause yet, it may not be a Firefox glitch, could be a hostile program.
Depending on which version you are using, there may be a backup of your bookmarks in a file on your PC. Do a search for any file with the word "bookmarks" in it.
If you find it, restore it. Then make regular copies of it to protect yourself.