Generally, the new FF is great. One small criticism - their GPU accelerated CSS animations are a bit choppy on mobiles (these a generally very smooth on chrome and Safari).
I tried it on Android, but a few of my app's users complained and a lot of them use iOS. You can try it out at https://usebx.com/app - just click try demo to get to where the animation is.
You'll find the page transitions are not quite as smooth in Firefox when compared with Chrome or Safari.
Well, as it says in the article, Firefox and Chrome on iOS are both just WebKit wrappers, because Apple doesn't allow other browser engines into their store, so I don't know what kind of black magic or bias or whatnot your users are experiencing.
As for Android, the new CSS engine (called "Quantum CSS" or "Stylo"), which landed with Firefox 57 on the desktop, should ship on Android with Firefox 59.
There's also "Quantum Render" or "WebRender" upcoming somewhen soonish. I'm guessing Firefox 60 or 61 on the desktop, so maybe again with a small delay then on Android, I don't know.
Also, noticed another thing - on Android, using FF nightly, I couldn't access a local network URL via FF (Unable to connect message), but could with Chrome - example URL http://10.0.130.64/path
