|This happens, when the bookmarks file named places.sqlite gets corrupt.|
So open Firefox, open bookmark manager and export your bookmarks to a file named bookmarks.html.
After that, go into the profile folder of firefox and delete the file places.sqlite.
Start firefox again.
Now firefox did not find it's places.sqlite, where all bookmarks are normally stored and searches this folder for a bookmarks.html file. With this file, firefox creates a new file named places.sqlite and imports all the bookmarks of the bookmarks.html file.
And voila, everthing is working again.
The original poster should always write the last response !!!
Let us know, if the problem is solved !!!