If your computer is infected by virus or malware, no matter the source, firefox will not be able to stay safe.

First, you will need to use Anti-Virus and Anti-Malware software for a deep scan. Only when your computer is clean, you should try re-install firefox.

I have an anti-virus program from my internet provider that detects and quarantines the virus which I then delete. I then go into programs and delete each item in firefox. I have used HitmanPro to make sure there were no other hidden malware or virus. I have installed Opera and Chrome with no problem.

if you are sure your computer is clean.

First uninstall firefox, if it can't be done, go to its installation directory and delete the mozilla folder. I understand you have done so. Please do this again if you have firefox installed at this moment.

Click "start" type "%APPDATA%" (all caps) and goto application data folder and delete mozilla folder from there.

Now reinstall firefox and see if problem is solved.

Troubleshoot Firefox issues caused by malware has some links to other things you can try running on your computer.

May not help that some antivirus clients still give false positives for the stub installer even though it has existed since Firefox 18.0, yet the same antivirus is fine with the full setup.

Www.mozilla.org/firefox/all

I uninstalled my ISP's anti-virus program and then installed AVG Free. When I downloaded Firefox, there was no problem. I also used HitmanPro and it did not detect anything either. When I re-installed the ISP anti-virus, (after uninstalling AVG) it quarantined the "Trojan" and disabled Firefox. Your suggestions were very helpful and helped me troubleshoot the problem. I am going to contact my ISP and advise them of the problem. I am very relieved to know it is not a virus and is instead a problem with the ISP anti-virus. Thank you all for your help!