Never had this problem. I’m using Firefox on Windows and Android with another search engine for years now.

Never seen this. Do you have some kind of browser extension or malware?

Do you still have the Google search engine added? I always fully remove it, since Searx pulls from Google anyways, I don’t really see the point in keeping it.

Nope, never happened to me in 10+ years of usage, except when completely reinstalling after wiping everything.