The friction is far too high. It's impossible to scroll more than one screen or so in a single swipe. It's maddening. I can't fathom why they didn't just use the OS default behavior.
FWIW, the release notes for Firefox for Android call out scrolling performance improvements in 3 of the last 4 releases. Might be worth taking another look :)
I have both Firefox and Chrome installed. I can't tell the difference between the two in terms of scrolling. On both I can flick and it keeps going for ages. It sounds like a bug to me.
It could have also been fixed. Last I tried was around a year ago.