They're maintaining 32 million lines of code, same as Chrome, on dramatically less resources. So if the question is how they manage to be so much more efficient in terms of ratio of resources invested to production capability (or insert preferred metric, LoC, market share, code line commits, security updates etc), I think it likely comes down to the breakthrough efficiencies of Rust, which they developed.
Rust was the backbone of Quantum, their monumental overhaul and modernization of the Gecko engine. Mozilla is way ahead of competitors in shipping production Rust code. Google is in C++, but taking baby steps toward also implementing Rust in bits and parts but with lots of security containering and interfacing with C++.
This is not correct. Servo predated Quantum. Quantum was never abandoned, it was completed and integrated into Firefox. Quoting from their page on Quantum:
>Firefox Quantum was a revolution in Firefox development. In 2017, we created a new, lightning fast browser that constantly improves. Firefox Quantum is the Firefox Browser.
Quantum took modernizations that were started as part of Servo but integrated them into Gecko, where they continue to live today. They include Stylo as you noted, but also WebRender, Quantum DOM, Quantum Compositor, Quantum Flow, as well as a host of rust libraries and tooling.
Firefox’s responsiveness, GPU acceleration, and memory-safety improvements are directly attributable to Servo's research being folded in.
So it is in fact getting the benefits I stated. In fact it demonstrates that Servo succeeded after all: the fruits of it were harvested, brought into Firefox and are a key demonstration of Mozilla punching above its weight with smart investments allowing them to be more efficient than Google.
Edit: The reply below is largely unresponsive, not acknowledging factual inaccuracies, and repeating points that have already been addressed. As I already explained, Firefox benefits from Servo to this day. The end of its support is regrettable but not a scandal nor even a demonstration of inefficient use of resources. Its benefits were rolled into the core browser which is maintained at a fraction of the cost of its competition.
There was a time when Mozilla worked on what is being now pushed forward under the Servo umbrella. 2017 was 8 years ago. Then in 2020 Mozilla laid off 250 employees, including pretty much all of the developers of Servo/Quantum and their security team.
And now Mozilla is sitting on that cool $1.3 B, burning $220-500 M/year on "software development" without telling anyone what it actually is doing with that money, and putting $0 into Servo.
Now, how come they burn $220+ M/year into software development and $0 on Servo?