[leetnewb]

Firefox can't compete with iOS or Android for what should be obvious reasons - it is structurally impossible. Also, the competing browsers are way better today than in Firefox's heyday. There is very little reason to use Firefox today outside of ideological.

[tiltowait]

Firefox (and its derivatives) is swiftly becoming the only place you can run full uBlock Origin. That's a good reason right there.

Ignoring adblock, I think you could flip it. Chrome and Firefox are basically interchangeable, so if there's little reason to choose Firefox, there's also little reason to choose Chrome.