I believe Mozilla was heavily involved with the creation of Rust, although that has now been transitioned to the Rust Foundation; not sure if that impacts them and/or what other projects they might have
Firefox
A community for discussion about Mozilla Firefox.
This is correct, and along side the Rust development, they also started work on a web renderer, in Rust, called Servo that at one point was considered as a possible future replacement for the Gecko engine. Around the time Rust transitioned to the Rust foundation, Servo was also pretty much abandoned by Mozilla, moved to the Linux Foundation in 2020 and then Linux Foundation Europe in 2023 where it is finally getting some steady development again. There is also some recent progress on building a browser based on Servo, although it will probably be some time before it's ready for daily use.
Some of the reason that Google makes a lot more money than Mozilla does is also, I think, tied up with some of the reasons that people take issue with Google.
They definitely could've been Proton, but they've just constantly played follow the leader into obscure things like making a new operating system instead of useful products.
Even when they do make something useful, it's normally tied to Firefox in a "you MUST use Firefox" kind of way, which is just so unnecessary.
And even if they were what proton is today (a thriving company that is profitable and doesn't rely on VC funding), I think it would still have money problems because of the egoist executives that take huge bonuses