Another thing working against Firefox on mobile is that it seems like every software update for Samsung phones resets the default browser/URL handler to Samsung Internet. Anyone not paying close attention will just click through the EULA and suddenly no longer be using Firefox.
I have a Samsung phone, and it's updated quite recently, but I've never noticed this.
I virtually never open Samsung Internet only because I virtually never open any web browser. Browsers launch as a side effect of something else. For example clicking on a link inside LinkedIn, Telegram, bank app help, etc.
When that happens, if a separate app gets opened it's usually Firefox Focus that opens for me, so I guess that means the default URL handler is Firefox Focus (must have set it years ago) and it's not being changed by software updates.
I have a history of being unlucky with technology, which is why I worked in QA before becoming a software engineer. I've noticed lots of jank w.r.t. Firefox and phone updates. YMMV. Firefox desktop updates have reset privacy preferences at least once in the last month or two, and Samsung Internet has made itself my default on top of Firefox at least two or three times in the last few months.
