EDIT: Oops, double post. Sorry.

EDIT2: Actually, I can use this.
Trying the 'Mark Threads as Read' option numerous times did nothing. Also, whenever I try to quick-edit posts, I get this:

[Image snipped 'cause it's not relevant anymore]

Ack. And this is only in Firefox, no other programs. I'm also getting problems on other sites with images not showing properly - any ideas?

EDIT3: Ok, it's not doing it anymore. Disabling that plug-in must have worked. Again, any passing mods - feel free to close this thread.