today I had that problem a second time. FF, without having updated, seems to ignore CSS of some sites (e.g. Jamendo, Heise) and displays them without any structure (all elements are shown top down). Me, I did not change anything regarding the configuration.

Any suggestions? I've tried for hours (checked all rules and exclusions, deactivated and removed all addons) at my other computer but had to remove .mozilla in the end.