What is the current value of the keyword.URL pref on the about:config page?

• http://kb.mozillazine.org/about:config
• http://kb.mozillazine.org/keyword.URL

If you do not keep changes after a restart then see:

• http://kb.mozillazine.org/Preferences_not_saved
• https://support.mozilla.org/kb/Preferences+are+not+saved

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• 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

aboutconfig: seemed to do the trick.

You paste: about:config into the firefox address bar.

Ignore the bit about 'here be dragons' humourous warning to be careful.

Scroll down to 'Keyword URL' - double click on it and change the text in the dialogue box. I changed it to http://bing.com/results.aspx?q= which means I use bing search but if you read the articles in Cor-el post then they give alternatives, I also ran spybot and malwarebites for goo measure.

Thanks

about.config method worked for me as well.

An item to note all commands that have been changed from default on the about.config window are in bold

Malware programs such as malware bytes do not correct the issue stated in the original question. They are always beneficial to run, but do not correct.