Interesting... Can you show the issue? How is the malware showing up?

I can't find the "program: Startfenster", so I can't uninstall it. I tried to find it out with "Bleach it" or "adwcleaner". But it hasn't be found by them. But every time I open my browser "Firefox", it's be opened at first and immediatly. But only in "Firefox", no in any other browsers. (Sorry for my English - I'm not a native speaker 🤷♂). I hope, I could explain, what I mean... Thanks

Try these. A screenshot of the issue would be helpful. https://learn.microsoft.com/en-us/sysinternals/downloads/process-explorer https://learn.microsoft.com/en-us/sysinternals/downloads/autoruns

Is a push notification? https://support.mozilla.org/en-US/kb/push-notifications-firefox

Here you can see the screenshot...