Greasemonkey has a massive security hole in it which, depending on the scripts you have installed, can allow any website to read the contents of your hard drive (this is the case as far as I understand it, please leave a comment if I have the details wrong).
This is very major. In addition to being a massive explot, it also means that Mark Pilgrim’s O’Reilly book-in-the-making Greasemonkey Hacks
is DEAD until we fix this, so here’s looking forward to a fixed version, although from what I gather it will require a large amount of work to provide a fixed yet fully-functioning GM. Good luck guys!
via Groovy Mother