Put another way, what problem is this new policy solving, and how big a problem is it?
With this step it follow Safari, which is already protecting users against third party tracking.
Is that a problem, however? Or more precisely, one that Mozilla wants to think is a problem and "solve"?
I use adblocking and such myself, but I think it should really be a personal choice --- browsers should just stay neutral. I have a suspicion that browser organisations taking sides in this will only lead to even more invasive tracking in the future, since this is a cat-and-mouse game. (Imagine if Firefox had adblock by default. It would just force adtech companies to come up with even more unblockable methods, since the defaults have changed.)
Websites can't do anything the browser doesn't allow. Or said another way, websites can only do what the browser was programmed to support. The browser is the decider.
Now the popups are almost always not new windows, but "pop-overs" inside the page itself.
Safari did and had to make multiple changes to ITP because criteo was fighting back.
It is always necessary to stay vigilant.
Browsers are user agents - they should behave as such.
Trackers only exist because of decisions they made (to store files on behalf of users that websites ask them to). They made that choice for users. Now they are realizing that isn't always the right choice and are looking to make a slightly different choice.
If reputation was really that important, these sites wouldn't have put up these low-quality ad networks in the first place. It's not like they didnt know what was running.
You mean this as a pragmatic choice, or moral choice? Because on a purely pragmatic level I somewhat agree with you - a popular browser making such decisions is risking either losing users, or furthering the cat&mouse game. But on the moral/ethical level, the browser is an user agent - providing features allowing users to enforce their preferences is a good thing.
Yes, but now it is not an educated choice, most simply have no idea they're tracked. Ask any person, "do you agree to being tracked?" Answer is obvious, so why not implement it in browsers by default?