Mozilla don't really care about mobile. The (too) small mobile teams do care, but the company as a whole doesn't - which mostly explains why it's so rough.
Firefox Focus is my go to browser on Android for 'just looking things up'. It's perfect for Wikipedia and IMDB (when someone points at the film you are watching and asks who the actor is). I only use another browser if I want up keep the page. No cookies, no bookmarks, no trackers
Sadly, Focus appears to just be another Chrome skin with some ui and privacy tweaks, and I think it's pretty telling that Mozilla did this rather than actually use FF mobile as the basis for this product. If you want to encourage browser diversity it doesn't really help.
I use FF Mobile because I want competition and I do like the features Firefox offers, but the performance and UX on Android are definitely lacking relative to Chrome.
Just go into Private Browsing in Android Firefox and you have essentially the same thing as Firefox Focus, except with Gecko underneath it and all the usual amenities of a full-featured browser.
Focus is meant for average users, who don't necessarily understand what Private Browsing does.
Having it as an Android Webview wrapper is nice, because it makes the APK really small. This way, users don't have to have two full browser APKs installed.
And well, it's not like it sways webpage owners one way or the other much, to have users use Firefox when they have all trackers and as a result essentially also all ads blocked. They don't make revenue off of those users, so why should they worry about making their webpage work for those users?
To me the UX is a major plus in FF on Android (albeit with plenty of rough edges in the more hidden features). But yeah, no investment in mobile performance sucks (but hey, they spent hundred of eng months on making desktop not suck, so yay I guess?).