As others have said, FF doesn't have a lot of leverage left to influence those type of decisions, but Safari might. Not sure what their position is on this proposal.
The one pager has a section on stakeholder feedback [0], but doesn't name them for some reason.
[0] https://github.com/RupertBenWiser/Web-Environment-Integrity/...
They should hunker down and make the best browser they can, implementing their best web. It worked 20 years ago, and in many ways the circumstances are the same. We have tech monopolies proposing ludicrous "content security" mechanisms. Where would Mozilla have been if they tried making some sort of half baked "less evil" form of Microsoft Janus DRM[1]?
People are going to get sick of how intrusive DRM is becoming, and there should be an alternative waiting for them.
Every person who has content they thought they purchased "expire" and be erased from their device, or who can no longer use their expensive projector after the latest mandatory update.
I evangelized heavily for Firefox in the 1.x days. People were sick of IE6, and were glad to have Firefox. I worked at a computer store and probably converted 100+ people.
Mozilla's revenue is proportional to usage so they need enough users to cover their development costs.
Wikimedia is honestly the only organization with the right ideology, the right business model, and enough money to do something like this sustainably.
FF didn't have leverage in 2005 but we're still somehow living in a post-IE world. Leverage and market share aren't a concern, community support is all that's needed. The issue is that Mozilla Corp have been rapidly burning community bridges at pace of late, topped off by the fact that 2005 Mozilla wasn't dependent on Microsoft for their income.
Full disclosure: I was employed as a software release engineer at the Wikimedia Foundation from 2015 through 2022.
Your username is the same as the initialism used internally to refer to the Wikimedia Foundation.. The WikiMediaFoundation: WMF