I tried to use FF on Android, and while it's capable and works rather well, perf-wise Chromium is just years ahead (I use Brave).
You can see it well on JS-heavy sites like Twitter, the difference is very easy to perceive with loading time, scrolling perf, and also with memory management (Firefox evicts pages from memory cache aggressively compared to Chromium; you sometimes switch a tab or switch an app, go back, and bang, it's gone and needs a reload); and I have a decent good phone (not top shelf, but a "high-mid" Pixel 3a, probably 60-70th percentile within Androids?).
You can see it well on JS-heavy sites like Twitter, the difference is very easy to perceive with loading time, scrolling perf, and also with memory management (Firefox evicts pages from memory cache aggressively compared to Chromium; you sometimes switch a tab or switch an app, go back, and bang, it's gone and needs a reload); and I have a decent good phone (not top shelf, but a "high-mid" Pixel 3a, probably 60-70th percentile within Androids?).