If new profiles become infected, there probably is malware outside of Firefox that is changing your browser settings, or at least there is an externally installed add-on.

Could you try the tools in this article: Troubleshoot Firefox issues caused by malware.

By the way, what software are you using to prevent your home page from being changed? Some settings protection programs may make it hard to remove unwanted settings.

I use the free version of Advanced System Care. Oh, and the spelling is with one r = venteeRo

The Advanced SystemCare "Surfing Protection" feature will roll back changed settings when you exit and restart Firefox, so if you find that your own settings changes are not saved, you might need to disable that feature temporarily.