I've seen this before.
This might help :
First:
Look in your Firefox Profiles Folder, and check to see if a new Profile folder has been added
See this page for: Profile Folder Location
How many Profiles are listed? If there is more than one Profile, then your Bookmarks are most likely still located in the profile you were using previously.
If you do have multiple profiles, then start Firefox using the original profile.
You can do so by right clicking on the Firefox Desktop shortcut
Select: Properties
Click on the Shortcut Tab
To the end of the Location field, add one space, then -p
"C:\Program Files\Mozilla Firefox\firefox\firefox.exe" -p
This will open the Profile Manager
Try each of the profiles and hopefully you'll find the Profile with the original bookmarks.html file.
If you find the original Profile with all the appropriate files, then in addition to the -p you have added to the Desktop Shortcut:
Add one space after -p then type the Profile name which contains the appropriate files.
It will be similar to: "C:\Program Files\firefox\firefox.exe" -p profilename
The Profile Name will be what precedes the random characters, e.g., ramona.jkl
I would also strongly advise making frequent backups of your Profiles folder. In the event Windows should hiccup, freeze, or should a reformat be necessary, you won't have to worry about losing any of your Firefox Profile data.
* source *
http://home.att.net/~cherokee67/fflostbkmk.html