If you are getting pages opening automatically, you need to check for malware since this may be caused by an infection. Try running a full scan using [http://www.malwarebytes.org/ Malwarebytes]. If it is ads on sites that you want blocked, you can use an add-on, [https://addons.mozilla.org/en-US/firefox/addon/1865/ Adblock Plus]

Do a malware check with a few malware scan programs.<br /> You need to use all programs because each detects different malware.<br /> Make sure that you update each program to get the latest version of the database.<br /> *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