Hi, have a work through this article and hopefully it will resolve your problem.

Also, every now and then you should run several mal-ware scans to make sure your system has no problems.

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

We had another thread on this last week: Had binkiland malware, removed it, now on my website another window is opened.

That user mentioned SearchProtect, which you also should remove because it can lock unwanted settings in Firefox, among other things.