Do you have any extensions (Tools > Add-ons > Extensions) like IE View that use IE to display web pages?

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

i have disabled all the Add-ons and the problem persists. It is not every time i open a new web page. Just occasionally IE will open the same page as just opened using Firefox.

The only Add-ons i have are AVG safe search 9.0.0.812, Bar discover 1.0, Google toolbar for firefox 7.1.20100408Wb1 , Java console 6.0.16, Java console 6.0.20 and update service 1.2.

As i say these are disabled at present and the problem persists

Do a malware check with a few malware scan programs. You need to use all programs because each detects different malware. Make sure that you update each program to get the latest version of the database.

http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware http://www.superantispyware.com/ - SuperAntispyware http://www.safer-networking.org/en/index.html - Spybot Search & Destroy http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page .......... See also "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

I also had the same issue as you, and it was from a site along the lines of go.tracking202.com. I ran a scan with the Maleware bit's and it found the infection and removed it, now my browsing is good to go.