AFAIK, Firefox is not Chrome-based anywhere.
On iOS it uses whatever iOS provides for webview - as does Chrome on iOS.
Firefox and Safari is now the only supported mainstream browsers that has their own rendering engines. Firefox is the only that has their own rendering engine and is cross platform. It is also open source.
Interestingly safaris rendering engine is open source and cross platform, but the browser is not. Lots of linux-focused browsers (konquerer, gnome web, surf) and most embedded browsers (nintendo ds & switch, playstation) use webkit. Also some user interfaces (like WebOS, which is running all of LG's TVs and smart refrigerators) use webkit as their renderer.
https://en.wikipedia.org/wiki/File:Timeline_of_web_browsers....
https://en.wikipedia.org/wiki/Timeline_of_web_browsers has tables as well.
Not technically "Chrome-based", but Firefox draws graphics using Chrome's Skia graphics engine.
Firefox is not completely independent from Chrome.
In any case, i thought chrome used libnss which is a mozilla library, so you could say the reverse as well.