I use a 2019 flagship phone (an s10e), and Firefox for Android is butter-smooth for me. So I cannot imagine why it would be janky for you with your multiple-times-faster modern phone?
Sounds like you're describing Firefox from around the time my phone was made (which was indeed slow and janky, and had lots of UI issues).
Sounds like you're describing Firefox from around the time my phone was made (which was indeed slow and janky, and had lots of UI issues).