I don't know what it was, but it made my Default Firefox profile glitch. I had to restart my computer and re-select my default after making the mistake of making a new profile. If any of you have the same problem, here's how you get back to the box. (firefox help file doesn't talk about it at all)
Go to run, then type 'firefox.exe -profilemanager' without the little quotation thingies. After you've restarted, you can re-select Default.