You may already have been infected and the malware may only work with Firefox 9 and not with Firefox 3 versions, so you hadn't noticed it before.

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

You may be correct, so I'm now running Firefox 3 again. The malware was eventually removed by PCTools Internet Security, but the price was severe degradation of system performance by the security program! When I attempted to uninstall it, the Uninstall program crashed. Eventually I got rid of it by deleting processes in Task Manager, and uninstalling again, only to find that something (either the rogue or the security software, had screwed up Windows, corrupted IE. Windows would not run any .exe files, including explorer. I eventually resorted to a System Restore, followed by a lot of reconstruction -- I had to download IE9 installer from another system to regain internet access at all.

I dream of getting my hands on the author of one of these rogues someday, and using my surgical skills to cut his balls off, with a dull scalpel.

Thanks for your assistance.