I don't think that checks out.

Firefox only exists because it's primarily funded by Google. It's funded by Google to ensure they actually have some competition and avoid becoming a Monopoly.

If they kill Firefox or otherwise make it unusable they'll be shooting themselves in the foot.

However, if it ends up being a bad experience that no one wants to use, well that's not on them and they have no responsibility to fix it.

What will likely happen is Firefox will also adopt this DRM.