Rust is a technical improvement, so it's exactly what many users are asking.
>who knows what they might discover?
They'll discover, just like Opera, that an abundance of useless features doesn't make up for a browser that is lacking speed, security, a clear design, ease-of-use and configurability.
No one is criticising Mozilla for coming up with Rust, yet if they didn't take the time to experiment Rust wouldn't be around.
So yeah, good on them, I'm happy for them to try voice recognition and other endeavours, who knows what they might discover?