At least half of those are patched Firefoxes, without telemetry and improved privacy.
Brave, Vivaldi, Edge etc are way more different from chromium than any of those from Firefox.
The thing is Firefox components are more tightly coupled. blink and v8 are easier to wrap in your own browser than gecko and SpiderMonkey.
Mozilla has been refactoring for ages improving the modularity of Firefox, but it may be already to late.
Python in the browsers seems like the only outcome worst than JavaScript in the browser.
It sends shivers down my spine.