> Third party cookies cannot be turned off without this replacement and for other things due to competition law and web ecosystem issues.

"competition law" is a problem for Chrome; as a browser run by a massive advertising company, interfering with other advertising companies raises antitrust concerns. It is not a problem Firefox needs to care about. (Also, it's not a problem that a browser with a tiny fraction of market share needs to worry about.)

"web ecosystem issues" is a fascinating euphemism. Let's cause more "issues" for advertisers.

> Ad supported content is worth something and eliminating that business model overnight would be bad as a bunch of things would be less accessible.

It's not going to go away overnight; it will take a long lingering time to die, and that time gets longer every time someone hesitates to kill it. In the meantime, as it becomes less effective, other models will become more effective.

If Firefox delivers a feature the AdTech industry would be OK with, then Chrome can adopt it and kill third-party cookies. Firefox already can block such cookies, but some legitimate sites may break (but developers don't care about Firefox). If Chrome blocks them by default, those sites will have to adjust.

Chrome is already delivering a (different) feature that they propose as a replacement for third-party cookies. That's not a reason for Firefox to adopt that API.