I'm going to go with the latter, but at best this is debatable and highly subjective depending on what matters to you.

> I have only seen the code of Chrome and it’s very Google-like C++, with truly enormous codebase.

I don't know where you are going with this; FF is a large code base too, uses servo (rust) and c++.

> Even Chrome did not fork Firefox back in the day and forked Safari.

> Electron did not use Firefox either.

Good for them? Never been interested in chrome/chromium or electron based apps.

I had always wondered why since Brendan Eich came from mozilla, forking from it and going their own way would be natural for them (imo), highly doubt that all of a sudden all the stuff he worked with for years became crap overnight and the decision was probably more political than anything, but who knows, just baseless speculation on my part.