Look in
C:\Documents and Settings\YourName\Application Data\Mozilla\Firefox\Profiles (hidden folder so, like the fs9 cfg, enable viewing hidden files)
There will be a folder there with random letters and numbers. Open that.
In there there will be several folders. In the root of the random number folder there will be Bookmarks.html and Bookmarks.bak. The Bak is the most recent backup, you could rename that with html and open it to see whether it's the list you want.
If not, look in the folder in there, appropriately named ... bookmarkbackups. You will see at least 5 backups there, usually the last 5 days worth. It does this automatically. As they are already html files, you can just open the to see if they contain your missing bookmarks.
I usually copy and save one somewhere else for safe keeping. Once you have the one you want, copy and paste it into the random letter and number folder, replacing what was there.
