hello AWJAB, since this can sometimes be caused by malware active on a system, please run a scan with different security tools like the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes], [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner] & [http://www.microsoft.com/security/scanner/default.aspx microsoft safety scanner]. [[Troubleshoot Firefox issues caused by malware]]

Try this: *Download the full Firefox installer and save the file to the desktop<br>https://www.mozilla.org/en-US/firefox/all/ *Start the installation with a double-click on the desktop icon