I use Disqus comments on this site, and I just had a problem where I kept getting the error "Disqus seems to be taking longer than usual. Reload?" with no comments or text entry box. I'm using Firefox 16.0.2, and I don't have any extra plugins enabled. A few are installed, but only the defaults are on. I read on the Disqus forum that it could be because of too many plugins (not here), slow internet (definitely not here!), and slow webserver (not here). The only other possibility, which is what I discovered was my problem, is a corrupted Firefox profile. I'm using Ubuntu, so my Firefox profile is located in my home directory in the folder ".mozilla". Note the ".", and by "." I mean the one preceding "mozilla", not the one at the end of the sentence! I moved (renamed to ".mozillazilla", actually) my folder instead of deleting it so that I still have my bookmarks, and so that I can easily restore it if creating a new profile didn't work. It did, and now comments load as they should.
Removing your ",mozilla" folder can be a pain-in-the-ass, make no mistake. That is where your bookmarks are stored, as well as your login information. I know all of my passwords, and I don't have a lot of bookmarks, so that isn't a big deal for me. If I want to, I'm sure I'd be able to selectively restore them from the old folder.
If you have the time and patience to remove files one at a time in order to isolate the one that gives this problem, please let everyone else know by leaving a comment below. If you can!