“Sufficient Permissions” Problem

Yesterday, I was using WP as usual in Firefox, when suddenly this page just popped up and I can’t get to WP at all.

It has to be a problem with my browser, because
a) My coworkers have no problems getting into WP from Firefox or Explorer
b) I can get to WP in Explorer

I’ve checked for updates, cleared cookies, fiddled with the permissions – all to no avail.

Can anyone help me with this?? Is there something I should be looking for?

On a less-pressing note, Firefox also stopped allowing me to upload photos in WP, so I’ve been going to Explorer to do this for a few months now. All the tech guys here are stumped, and again, no one else at work is having these problems. I also tried all the things up above, plus I downloaded a java and flash update, as well as uninstalling and reinstalling Firefox. Which doesn’t help, because it remembers your computer and all the screwed-up settings.

GRR. Help, please!