Was that a legit pop-up from Windows or your security software or did it look that it might be coming from malware? Do a malware check with some malware scan programs.<br /> You need to scan with all programs because each program detects different malware.<br /> Make sure that you update each program to get the latest version of the database before doing a scan.<br /> * 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 and [[Searches are redirected to another site]]

Also where were you trying to download Firefox from as was in from mozilla.com or mozilla.org or someplace else?