according to entries on other forums this is occuring when a program called bProtector.exe is running on your pc. download & run hijackthis and fix the service entry for this piece of software to get rid of the problem...
also have a look at the How to fix preferences that won't save troubleshooting article (especially the section about user.js if the homepage is the only setting that won't stay after a restart of the browser)
Some security software has virtualization features that can cause problems by protecting and restoring files in the Firefox profile folder.
I have the same problem..Please if anyone has another solution let me know. I have done the about.config and it keeps on coming back on..