My machine is in the upper-mid range with a TR 1950X + Vega 56, so I can’t imagine it’s a spec issue.
I’ve read the entire Arch Wiki article on Firefox performance [1], ensured that hardware acceleration and other performance settings/flags are enabled, and tested different configurations of theses settings. Nothing made a discernible difference.
Chromium, even with hardware acceleration disabled, is dramatically more responsive than Firefox.
I have been very tempted to go back to Chromium. Ideologically and privacy wise, I really want to support Firefox, but I can’t help craving a lightning fast UI.