Should firefox be running js and xml files? And should it have a chrome folder?

I would bet money that something is funky with your profile. Since you didn’t specify what OS you are using you can try to find it. I would start here. Close Firefox and move the profile folder to your desktop so you can put it back later if that doesn’t help. See if Firefox works with a clean profile. It will make a new one for you if it can’t find your old one. You will loose all your bookmarks and passwords. That Is why I suggest saving the old one.

You might very well be right, I already had to restore my bookmarks a couple of weeks ago but hadn’t expected any more problems when everything looked ok after the first couple of days. I’ll try salvaging my profile and I’ll probably reinstall firefox anyway.

And keep in mind that extensions are mostly js and xml files. One of those could be bad too.

I would indeed guess it to be an extension that is badly written, so you might want to check those.

Also, chrome is not Google Chrome: see UI chrome vs. Google Chrome. That folder at least is perfectly normal :)