Mozilla seems to not want to interfere with online advertising practices.

Thanks, I will. I've been using the Internet since before online advertising became a big deal. I've run web sites of varying scales, often with original content, sometimes with original content that cost a lot of time and/or money to produce. I've also contributed widely to many more web sites and other online forums. I've paid for things online. I've charged for things online.

And I've never once, in all that time, relied on ads to fund any of my or my various businesses' contributions.

Online advertising has served a useful purpose in some cases, and I sympathise with those who have chosen to rely on it as a funding model and are now losing out because of ad blockers and the like. But online advertising has also led to huge amounts of ad-ridden junk clogging up any forum it can invade. It has led to serious degradation in both the performance and the security of the greatest information-sharing medium in the history of the world. Perhaps worst of all, it has led to a culture where other ways of compensating those whose work we truly value and of discovering new material of interest are a lot harder than they might have been. None of those are positive influences, and I'm not at all sure that online advertising hasn't done far more harm than good overall, even taking into account the great value that some ad-funded content and services have offered to some people.

> essentially all of the ad supported sites I visit are diversions

The web existed fine before ads, and could exist just fine (if not better) after ads.

While I would love to browse the web with all security and privacy features enabled and things like JavaScript disabled, it breaks too much. The middle ground between security/privacy and user experience/convenience is different for everyone.

My compromise now is to use uBlock Origin (virtually never breaks anything), HTTPS Everywhere (on rare occasion breaks a site), Self-Destructing Cookies (by design cannot break sites), and 3rd-party cookies disabled.

The only thing that banning 3rd-party cookies broke was CapitalOne360's gateway into regular CapitalOne, but they even managed to fix this in recent months.

The Facebook "Like" button for starters.

Is that user-hostile? Is that important?

It's in the eye of the beholder, but if Firefox "doesn't work" for a large tranche of non-technical users, that's a big problem.

It's also not clear how much it would achieve. It's not that difficult to turn a 3rd party cookie into a 1st party one.