Actually for the Browser developers (Google, Firefox, Microsoft, Opera, ...) it doesn't matter much if the "browser mining" is done because the user wants to mine or he just ended up on an infected website.
Since most people surfing the web are not educated about crypto mining, the browser mining has a much better chance to be malicious than intended.

All this make browser mining mostly a no-go, since there's a good chance the browsers will develop a safety guard against such miners.