You can check for recently installed suspicious or unknown extensions. *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes ---- Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. All these programs have free versions. Make sure that you update each program to get the latest version of their databases before doing a scan. *Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php *AdwCleaner:<br>http://www.bleepingcomputer.com/download/adwcleaner/<br>http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml *SuperAntispyware:<br>http://www.superantispyware.com/ *Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx *Windows Defender:<br>http://windows.microsoft.com/en-us/windows/using-defender *Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html *Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan You can also do a check for a rootkit infection with TDSSKiller. *Anti-rootkit utility TDSSKiller:<br>http://support.kaspersky.com/5350?el=88446 See also: *"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked *https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware

'''[https://addons.mozilla.org/en-US/firefox/addon/blocksite/ BlockSite]''' {web link} BlockSite is an extension, which automagically blocks websites of your choice. Additionally, this extension will disable all hyperlinks to these websites, by just displaying the link text without the clicking functionality. ------------------- '''[https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/ Adblock Plus]''' {web link} Blocks annoying video ads on YouTube, Facebook ads, banners and much more. Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).