Starting with a new profile.
If I change the default search engine and restart Firefox, I’ll be using my engine of choice.
If I setup the html autoexport and restart Firefox once, same.
If I restart a second time, it’s Google.

Switching the branding from openSUSE to upstream and creating a new profile solved it.

I’m using Firefox 62 from the mozilla repo so maybe I should have switched from the start?

I’m talking about this by html autoexport: https://support.mozilla.org/en-US/questions/1176242