One or more of the following should do it...
Clear your browser cache and unwanted cookies. Ccleaner makes this easy:
http://www.piriform.com/
Activate the Firefox settings to block pop-up windows, reported attack
sites, and web
forgeries
Install the Flashblock and/or NoScript add-ons in Firefox.
If you're running windows, install the MVP HOSTS file:
http://winhelp2002.mvps.org/hosts.htm
Scan your computer with free Malwarebytes, Superantispyware, and your
updated antivirus software.
--
J.Q.P.
(XP Home SP3, FF3.6.18 default browser, FF5.0_portable with FF3+ theme,
Chrome11_portable, Opera11_portable, Iron11_portable, Maxthon3_portable,
Seamonkey2_portable, IE6, Outlook Express default mail/news)