Better Safe Than Sorry

Firefox Greasemonkey Targeted

A new type of malware that collects passwords for banking sites is in the wild. In this instance it only targets Firefox browser through the popular Greasemonkey script. The malware uses JavaScript to identify some 100 financial web sites (including PayPal). It then harvests logins and passwords which are forwarded to a server in Russia.

So, short of disabling or uninstalling Greasemonkey your best defence is the usual: do not download anything, including Firefox add-ons, from any site other than Mozilla's, do not visit dubious sites located in dubious domains (such as .ru) and always have your firewall, anti-virus, router and brains active ;)