They have no market influence. They have maybe ~10% of the market globally (I've seen figures between 5-15%), and that's primarily desktop - which is decreasing daily. On mobile it's even worse (probably less than 1%).
Any influence they have solely extends to the desktop, and that's not the primary way people are interacting with the internet nowadays.
That's not a killer feature to the market: I bet 99/100 people don't know what DRM is or what it stands for. They just care that they can watch videos or not.
For better or the worse the overwhelming majority of browser users don't know, care, or have any idea about how the internet is standardized, how DRM works, and why it matters to them.
Indeed, that would kill Firefox once and for all.
I use Firefox and almost never use another browser but I'm afraid over time, it's share of the market will fall. This news makes me fear so even more. I do hope I am proven wrong though. I've seen one monopolist fall. I do hope I see many more.
In other words you have no idea what you're talking about, and why should anything else you say be treated any differently?
The user cares about access to content. The user does not care about DRM. The user does not care about corporate interests. Ad blockers are proof of this. The user wants what they want, and the people who provide that to them with the fewest hassles are the ones who win.
Everyone needs to appreciate that "cost" is a gigantic hassle to most people, no matter how much money they have. The concept of owning their content is another big consideration for people, which is why we saw "rental" models for video streaming fail in the past compared to "ownership" models.