I lost all of my bookmarks not too long ago-it was a mess.  I had to rebuild all my sweeps bookmarks from scratch! 

Then I found an add on for Firefox called Foxmarks-it backs up your bookmarks in case you lose them in a crash, etc. 

The other thing I found that was useful is that I can sync my desktop bookmarks with my laptop bookmarks (or any computer for that matter).  I had wanted to have my sweeps bookmarks on my laptop if I traveled or wanted to enter sweeps while watching TV in the living room. 

Good luck, Jeff