Uninstall Greasemonkey altogether. At this point, I don't trust having it on my computer at all. I would think that whoever is in charge of addons.mozilla.org should immediately remove the Greasemonkey XPI and post a large warning in its place advising people to uninstall it.
Mr2001 writes "A recent thread on the Greasemonkey mailing list suggests that the popular Firefox extension is fatally insecure. It seems rogue pages can read any file from your disk and send it to any site, using an XmlHttpRequest. Time to uninstall GM?"