Go to the Firefox 3 Bar Menu --> Help ? --> Troubleshooting Information Page and take a look in the Accessibility section if accessibility is set to "true" there. if yes, go to the Firefox 3 Bar Menu --> Options --> Privacy & Security panel and under Permissions check the setting to Prevent Accessibility Services from accessing your browser. Restart Firefox Please let us know if this solved your issue or if need further assistance.

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10 Do a malware check with several malware scanning programs on the Windows computer. *https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Please scan with all programs because each program detects different malware. All these programs have free versions. Make sure 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>https://www.microsoft.com/security/scanner/en-us/default.aspx *Windows Defender:<br>https://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>https://www.kaspersky.com/security-scan You can also do a check for a rootkit infection with TDSSKiller. *Anti-rootkit utility TDSSKiller:<br>https://support.kaspersky.com/viruses/disinfection/5350 <br>https://support.kaspersky.com/viruses/utility See also: *"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked