Firefox is not able to block some pop ups when I am accessing some websites

Do a malware check with a few malware scan programs. You need to use all programs because each detects different malware. Make sure that you update each program to get the latest version of the database. http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware http://www.superantispyware.com/ - SuperAntispyware http://www.safer-networking.org/en/index.html - Spybot Search & Destroy http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page .......... See also "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked and [[Searches are redirected to another site]]