I can't speak for Mozilla at large, but I've had the pleasure of witnessing both Mozilla's Rust and Servo teams at work and can assure you that they are at the top of their league. To pick just two examples, Alex Crichton is an unstoppable machine ricocheting around the compiler, standard libraries, package manager, various miscellaneous tooling, and dozens of libraries in the broader Rust ecosystem leaving patches in his wake (all while finding time to perform legendarily detailed code reviews); meanwhile, Patrick Walton is an awe-inspiring graphics programmer and browser engineer whom I am convinced is among the top five humans with back-to-front understandings of the CSS specification, and by now is likely the world's foremost expert on cross-browser CSS quirks and edge cases.
TL;DR: I'm a squeeing fanboy for a lot of the people in Mozilla Research.
Well, you have a point but you see, both Rust and Servo are at the nascent stage. We still have to see widespread adoption of Rust. Servo is definitely way behind any browser engine in terms of features and specs and rewriting from scratch might also introduce new bugs(happens with every software product of considerable size). To summarise, both of these are very nice and ambitious goals but I really hope they turn into something nice rather than just an ambitious project(Servo).
TL;DR: I'm a squeeing fanboy for a lot of the people in Mozilla Research.