For regular consumers, I'd say the biggest value proposition for Firefox on mobile, at least on Android, is the support for browser extensions such as uBlock Origin, and thus mobile ad-blocking.
As an example, there's currently no straight-forward way for the average Joe to set up ad-blocking on a mobile device (excl. DoH/DoT using PiHole, NextDNS, etc.). Many non-technical users are, however, familiar with the usage of ad-blocking extensions in their desktop browsers. They might not know the nitty gritty of how ad-blocking works, but most people seem to have one installed. Installing and using such an extension is just as seamless on Firefox for Android as it is on a regular computer.
Edge on both Android and iOS has Adblock built in and Safari on iOS can have ad blocking very easily enabled with a content blocking app like AdGuard. Firefox is arguably harder to set up for ad blocking than either of these.
Yeah, I was only speaking to Android in my post, and iOS is a different beast with different restrictions when it comes to browser implementations. Is Microsoft in any way competitive or innovative in the browser sphere? I haven't used Windows for ages so I'm out of the loop there.
If AdBlock is a built-in feature in Edge on Android, I assume you still need to opt-in through the settings (e.g., Settings -> Enable AdBlock), no? In which case the setup is Firefox is similarly easy: Addons -> uBlock Origin. Perhaps a bit less intuitive for an average user, but still very straight-forward to set up.
As an example, there's currently no straight-forward way for the average Joe to set up ad-blocking on a mobile device (excl. DoH/DoT using PiHole, NextDNS, etc.). Many non-technical users are, however, familiar with the usage of ad-blocking extensions in their desktop browsers. They might not know the nitty gritty of how ad-blocking works, but most people seem to have one installed. Installing and using such an extension is just as seamless on Firefox for Android as it is on a regular computer.