Do you mean that browsers implementing this will force website owners to make their sites work with tracking domains delayed? This does seem like a nice side benefit.
I imagine Mozilla is in a similar situation: if too many websites block, they will have to disable the delay or start whitelisting trackers if they do not want to loose users. That is, unless other browsers follow their lead here.
Prisoner's dilemmas all around. It's going to be fun to see what we'll end up with, although I'm optimistic as I haven't heard complaints about this yet, but then again I wouldn't notice any difference myself as I'm already using NoScript.
Apparently Firefox is sitting at 6.1% market share right now[0]. Far behind Chrome and Safari but still quite significant.
[0] https://amosbbatto.wordpress.com/2017/11/21/mozilla-market-s...