Tracking scripts should be blocked by default, not just delayed. If a user has some strange desire to be watched, give them the option to opt-in to their browser unblocking tracking scripts/domains.
There is in fact a preference to do that: Settings -> Privacy -> Tracking Protection, set to always.
It breaks some reasonably popular sites, which is why it's not on by default across the board right now.
As things stand, it's a hard sell to have a browser do something that breaks sites that used to work. Most users tend to not be happy about it. This is definitely an area worth pushing on; the question is how best to do it.
Mozilla could maybe afford to pull something like that, if they had the majority marketshare, as then webpage owners would have to deal with their decisions in order to still make any revenue at all, but well, they don't.