You should do the following:

Scan your Computer for Malware

• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Microsoft Security Essentials (A good permanent anti-virus if you don't already have one)

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Reset Firefox

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thanks for that advice tylerdowner. I did it and it seems to have worked. I still don't know how this malware appeared. Must keep an eye open for it in future.

thanks

The "removecomputermalware" page linked in the previous post includes complicated instructions and tells you, Make sure that you stick to the instruction, or any slight mistake will deliver undesired PC dysfunctions. Anytime you need professional help, you are welcome to contact 24/7 online computer help by starting a live chat here. ... which links to a support service that charges $69.95 per service incident.

Instead of following instructions on questionable Internet sites to remove unwanted or malicious software, see these KB articles instead:

• Remove a toolbar that has taken over your Firefox search or home page
• Troubleshoot Firefox issues caused by malware