bookmarks is not letting me save or do anything on it anymore.
My Mac OS X is old and does not allow newer versions of ff. but has been excellent with this version until this sudden problem.
A possible cause is a problem with the file places.sqlite that stores the bookmarks and the history.
You can also try to repair the places database with this extension: (the extension isn't compatible with Firefox 3.6)
You can use this button to go to the Firefox profile folder: