What Firefox was doing 4 months after Android 1.0 GA'd would indeed been unlikely to have made a dent in mobile share compared to what effort was going on once Android had a billion users. Why put all of that effort in before something is even used to just then let it rot for years anyways? In the end, they ended up spending the resources to refresh it in 2019 anyways - by which time billions had already decided Firefox was just a battery hog and slow on mobile.

It's a sad story because Firefox was so good on mobile when nobody had a chance to use it then it was crap when they did. On desktop Firefox is still the #1 non-bundled browser, things went so poorly on mobile they can't even come close to that today. In a parallel universe timings were inverted and Firefox may have even had more users on mobile than it does desktop today.