When a word has two meanings you can claim "you explicitly said it!!1" but that doesn't make me having actually meant the other thing that I didn't mean, particularly when the original sentence makes a singular meaning clear: nobody can build anything on Chrome, why'd Chromium then suddenly mean "Chromium and any code modification you can make to it" and not simply "Chromium the browser as it is"? "Chrome/ium" referred to the two Google browsers, not forks that modify the underlying code, like Vivaldi which obviously diverges and is its own thing. The comparison wasn't Firefox vs every possible browser built on Chromium. If you want to compare Firefox to Vivaldi specifically, sure, I'll trust that Vivaldi fulfills your special wish if that's what you're saying, but that's a different conversation
Not really, you've explicitly said this
> Yet it's still more customizable for users than Chrome/ium is
And then rejected the fitting comparison: Firefox (the browser) is not more customizable than Chromium-Vivaldi (the browser)
I also don't see how the engine used for page rendering is relevant when discussing UI