The Security Mentor

This isn't, directly, a "take over your computer" kind of problem but it could contribute to one. Secunia has found a problem that lets a malicious web page read big chunks of your computer's memory. I've run their online demo. It showed me leftovers from my surfing and email history. These could easily have contained passwords.

There's no fix yet (UPDATE: the developers have successfully tested a fix which will be in the next release), and the workaround really hurts functionality. The really lazy approach would be to ignore the problem and hope a patch comes out before bad guys start using the vulnerability. That might actually work. The next hardest approach is to install a browser extension like Pref Buttons or Preferences Toolbar and add a checkbox to your info bar to turn "Javascript" on and off. Leave it off except for trustworthy sites that need it, like GMail for example.