Mozilla / Firefox isn't lacking in new technology. Firefox has made far more aggressive under-the-hood improvements than Chrome over the past 5 years.

Rust, WebRender, Stylo, Pathfinder, wgpu, Dav1d, asm.js (which resulted in WebAssembly) etc.

And they helped bootstrap a lot of efforts that benefited everyone massively. Take the list above and add: LetsEncrypt, Cranelift, AV1, Opus, WebGPU, Wasmtime

Plus tooling like the reverse debugger (https://rr-project.org/) and sccache and Bors

Less promises, more keeping them.