My Computer
Folder Options
View
Select "show hidden files and folders"
Apply
OK

Then go to:

C Drive
Documents and Settings
Click the folder for your profile.  I call mine "Linda"
Open "Application Data"  (it is a faded out folder because it was a hidden one)
Open Mozilla
Open Firefox
Open Profiles
Open the next folder
You have now arrived where your bookmarks.html file should be. 

If you have a bookmarks.html file in there, double click it and see what shows when it opens. If your bookmarks are gone it will show only the default ones that came with mozilla.

Look for a folder called "Backups"  or "Bookmark Backups".  If you have one of those, you should find backed up copies of your bookmarks.html file from prior days.  If you don't have something like that, then your bookmarks are really gone  unless you happened to have saved the .html file to a CD.   After I lost my bookmarks to that weird bug, I now go once a month and save the bookmarks.html file just in case.

Oh yes. When you're done. Go back to Folder Options and change the setting back to "hide hidden files and folders" again.  You really don't want them showing just in case you get delete file/folder happy and accidently delete something you shouldn't  :)

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi