browser history problem has returned

On 2/25 I reported a problem - that my browser history vanished after one day. Original report (question 188806) is:

"Using Ubuntu 11.04 updated and firefox 10.0.2. All was ok till I updated about 1 week ago. The next day my browser history disappeared. If I reinstall from a backup I can access all previous history stored in the backup but again all browser history vanishes after a day. I reinstalled the entire system and my home directory but same thing happens. Firefox preferences are set to "use custom settings for history", I cleared the cache, and my config files appear ok but ?. Tried running Clam AV and that showed no virus but it kept showing 99% complete and never finished. Can anyone help?"

Received advice to move firefox to firefox.old and reinstall the browser since the problem might have been due to a config conflict. Seemed to work but tonight, after two days this time, the browser history again vanished. I am able to reinstall with a backup but problem persists. Preferences are set to 'Use Custom Settings' and 'Remember Browser History'. Anyone have a suggestion? Thanks.