It sounds like some other add-on got installed. You can try to troubleshoot and narrow down the cause with the instructions here - [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] Or you can reset Firefox. Instructions here - [[Reset Firefox – easily fix most problems]]

Do a malware check with some malware scanning programs on the Windows computer.<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 their databases before doing a scan.<br /><br /> *http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware *http://www.superantispyware.com/ - SuperAntispyware *http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner *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 You can also do a check for a rootkit infection with TDSSKiller. *http://support.kaspersky.com/viruses/solutions?qid=208280684 See also: *"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked ------ You can look at Adblock Plus to hide double underlined IntelliTXT type pop-ups. * Adblock Plus: https://addons.mozilla.org/firefox/addon/adblock-plus/ You need to subscribe to a Filter list (e.g. the EasyList). * http://adblockplus.org/en/subscriptions * http://adblockplus.org/en/getting_started