Chrome v Firefox on mobile (android at least) is pretty noticeable, but in a
good way IMHO. Firefox on mobile supporting extensions makes it 10x better out of the gate, but there are also little thought-through things like not having the horrendous "pull down from top to refresh" which 9 out of 10 times I trigger is an accident and not at all what I wanted.
I think this is actually a good example of where Firefox could really make a difference on desktop. Introduce a very powerful extension framework, allowing things like what Chrome is removing in manifest v3. Killer extensions will be built and people will switch for that. For the users who would inevitably install malware extensions, there will always be Chrome. Firefox doesn't need 100% market share, just one big enough that it can't be ignored.