Spoofing bugs seem to be the MRSA of browser flaws - none of them are safe from the latest hacking ability, not even the version 1.0.5 of Mozilla which is still in beta format. It doesn't help that two browsers had already been updated for other flaws yesterday.
Secunia's website is offering a test along with the basic report. It's more important than ever to clean out your browser cache to at least minimize the amount of information which could be stolen if the worst happens - and don't click on that amusing round-robin email with an attachment which might pass for communication from some “friends” of yours.
Visit Secunia here and test your browser.