Adware

I have this annoying problem in firefox, every now and then my webpage changes automatically to adware sites, toplist, porn etc.

I've ran adaware and spybot and even deleted firefox and reinstalled. Also looked my startup programs for anything unusual.

Any idea's please?

Delete everything in C - windows - prefetch after you uninstall firefox. also delete the firefox folder in programs and

Have you installed the AdBlock extension? It might be worth also installing the NoScript extension.