Hi RichyN,
Welcome to the forum!
Prior to installing FF 3.6 did you uninstall the previous version?
Failure to do so can sometimes cause minor glitches like the one you are currently experiencing.
Try uninstalling ( I would recommend using the free version of Revo for this:
http://download.cnet.com/Revo-Uninst...=dl&tag=button) and then do a clean reinstall to see if that fixes the problem. I would also recommend installing the FF add on FEBE that allows you to backup your FF profile including all your bookmarks.
Hope this helps.