Actually, what is the reason that Firefox seems to be preferred over Chromium? Is it the license? The control Alphabet has over it?

One has to agree that there is a lot more money poured into chromium, the code is more modern and easier embeddable, it is more feature-complete.

Though, it’s good to have two independent browser engines and a non-profit (+for-profit subsidiary) dedicated to a free, open, user-focussed browser.

Edit: both have open source licenses. Chromium seems to permit basically anything. MPL2 seems to enforce derived works to also be open source.