[cd34]

If I recall, there is a strangely named directory that contains your 'current' data... it will look something like:

9116o1wk.default and will be in a user preferences directory. Search your harddrive for bookmarks.html -- it should find your current one and the old one.

Shut down firefox, rename the current one, copy the old one to the new directory, restart firefox. Make sure you don't delete the old copy just in case it doesn't work properly, you'll still have the copy.

There is a way to do it in the registry where you rename the data store location, but, I have found copying the files a little easier. Make sure firefox is not running when you do it because it caches some of those files and will rewrite them.