Okay folks... this page is a fucking godsend. Most of it is stuff you'll probably want to skip, but two add-ons in particular are a must for safer Firefox surfing.
Blocksite and Adblock Plus (under Identity and Privacy halfway down the page) are brilliant.
Blocksite lets you blacklist specific sites that bug you, be they popup, ads, or otherwise.
Adblock Plus actually lets you SUBSCRIBE TO ADVERTISER LISTS THAT BLOCK MOST EVERY AD. Even if one slips through, it add an option to your right click menu to NEVER LOAD THAT AD IMAGE AGAIN!!!!
The main way viruses like Virtumonde propogate is through these fucking popup ads... so take a few minutes to protect yourself. You won't regret it.