The person who posted this question as the first, just found the solution for her own problem. Through options I reïnstalled the original start page. Now the problem is solved for the moment!

But the problem WHY it happened is still there of course........

Maybe someone else can help here because it's not nice when it happens over and over again.

The problem is now taken over by this website!!! Every time I start Firefox I get this one instead of the original starting website.

This bug seems to me an inside problem for the programmers!