Digging a bit in this forum I have found a solution from another thread. This worked for me, now the search term stays where it's supposed to be.

Go to about:config and switch browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar to false.

Yeah thanks, it worked. I did some digging too myself. Crossed that page too, but didnt think much of it. Thought it might have been something from userchrome.css customizations, so I turned my search towards this. When I came up empty, I tried your solution and it worked.

Damn mozilla, every major update they shove down our throats unwanted "improvements" and slip undocumented changes under the table. Every time they post a new update I shake like a leaf that they 'll have screwed up the interface AGAIN. A week ago I went through hell to fix browser appearance after FF89 update crap.

I swear, one of these days, I'll [prolly permanently] switch to OperaGX.