Because Firefox has a tiny user base and nobody is going to follow their standards as long as other browsers do enable third party cookies. Also, there are alternatives to third party cookies for most use cases, they're just more difficult to implement.
Neither Google, nor Microsoft, nor Apple seem to care much about re-engineering third party cookies. Until that changes, any attempts from Mozilla to change the standards is a waste of time and effort, really.
Neither Google, nor Microsoft, nor Apple seem to care much about re-engineering third party cookies. Until that changes, any attempts from Mozilla to change the standards is a waste of time and effort, really.