Edit: Getting downvotes for this honest question. I didn't realize that browser rendering engines held that much control. Apologies for the silly thought.
This is like asking why Pepsi doesn't just copy Coke's recipe.
It's cool to have multiple implementations but this analogy doesn't work since browser rendering engines are trying to produce identical results. You wouldn't say that PyPy exists as an alternative to Python, would you?
I think you would if Python (proper) was controlled by an anti-competitive information stealing superpower which is becoming increasingly disliked.
Alternative backends to Python would be very important. Ensuring that the language is still usable in the event that the primary contributor goes full-tilt evil.
With that said, i don't think it matters (personally) if Mozilla has their own engine _or_ browser, in the most strict sense. What matters is that both of those things have invested parties capable of forking and/or maintaining free and open source versions of those things in the event that Chrome (ala Google) goes full evil.
It does seem that maintaining your own browser and rendering engine seem effective ways to ensuring you're capable of carrying the torch should Chrome disappear tomorrow. Hypothetically they could just maintain/develop directly into Blink and Chromium.
The purpose of Firefox doesn't exist without Gecko, they both are to serve as an "independent" alternative force in the browser space.
Firefox gutted all of their internals with project Servo. If they had instead integrated Blink would it have been any different?
I always think it's interesting what things people want to have diverse ecosystems with competing implementations (browsers) and what things people consider that an unnecessary duplication of effort (Wayland compositors).
If you go into threads about Wayland the overwhelming public opinion is that having lots of compositors is silly. And then you go into threads about browsers the overwhelming public opinion is that having multiple browser implementations is sacred.
Just because they're failing at it doesn't mean they're not trying (AMP, needless degradation of Google services in non-Chrome browsers, etc). They only have to succeed once.
If Firefox became a Chrome skin then sure, v bad for the web. But if Firefox internally used Bink and V8 it's not really all that doom and gloom.
Happens all the time. Without Webkit and Gecko, the web would simply be "whatever Google wants to do". Having multiple browser implementations helps balance out whatever Google's agenda is at any given time.
The reason you have multiple implementations of JS and rendering/layout engines is because they provide a specific technical benefit, not a political one. The browser built on top doesn’t have to be anything like Chrome.
Safari is the only browser that has any significant uptake (~20%) and Chromium was forked from WebKit, so all Chromium browsers already share a good chunk of their foundation with WebKit. You could say that we really almost have a WebKit monoculture since Firefox, the only non-Chromium/WebKit browser only has 3.65% of the market. [0]
Heck, the vast majority of Internet servers and most of the clients are running on the Linux kernel but nobody is complaining about that.
I'm sure there are many backend libraries, parsers, etc. that are used by both Chrome and Firefox, but they're unlikely to replace significant components like that.
https://en.wikipedia.org/wiki/Mazda#Partnership_with_Ford_Mo...