I mean, they did a lot of improvements over time. ASM.js which became WASM, with fast bindings, Webrender, new JS engine, the memshrink project are ones that jump out at me. From the wpt.fyi interop stats year over yearit's pretty clear they are constantly working on implementing new specs.

But IMO everyone is chasing Chrome or just using their engine now. Their engineering team is apparently 10x that of Mozilla.

And, back when Chrome was rolling out they used their dominant position online very aggressively. Google sites worked best in Chrome, period. Chrome was pushed on google. Google tech demos, similar to Microsoft ones, worked best in or only in Chrome. Android was a big Chrome advantage too. Chrome was heavily advertised, pushed as an install bundle in things like Adobe.. I'm not disagreeing Mozilla made some poor decisions but I don't think they had much of a chance regardless.