alt Hacker NewsI 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).
Had dailied redmi note 12 4g, with debloat, ublock and selective uscript block. Many js/media heavy websites (that needed to have their js enabled to be viewed) lagged under firefox