HUH. Ok, I did some testing with my extensions and found the problem, since I don't use any site skin. (I had tested with some of my stylus stuff, but that didn't cause the problem and I didn't dig any deeper)

It's the DW tag recovery extension for firefox that's doing it. I'm not sure WHY as it shouldn't affect anything like that, it's just a form recovery tool.

If that's the case I'll just have to deal with it, unfortunately.