FEBE (Firefox Environment Backup Extension) recently went through an upgrade (probably V. 6.0) and provided a warning that existing users should reset their backup options. At the time I was busy and thought: I have my options set, I don't want to change them. That was a mistake - after a FF 3.5 hiccup last night I found that in my case the new version indeed ignored prior profile backup options and by default was only backing up extensions and themes. So in FEBE V 6+ examine your backup options and reset them where you want. (I recovered from my FF 3.5 problem, which wasn't major, by means that didn't exactly make logical sense, but that's Windows computing for you.)