I feel like nobody will have to consciously do anything in particular, with the current way how things are going.

- Chromium is the modern IE and developers will primarily be on the hook for supporting it, Firefox support will be an afterthought so some sites will just be broken, moving more users over to Chromium.

- The Firefox marketshare is dwindling, it's likely that the users with proper ad blocking will eventually be a rounding error and therefore quite inconsequential. Especially if there are any more ad-related APIs pushed by Chrome that make users more profitable (e.g. Topics API).

- Even among tech enthusiasts, Mozilla in particular doesn't have very good reputation (e.g. how much they spend on actually improving the browser vs other initiatives) and I don't see the marketshare of Firefox skyrocketing, unless something big happens. New competitors like Ladybird are also niche, though it's a really cool project.

- If Apple ever moves over Safari to Chromium, like Edge did, then that effect will only be amplified.