While I strongly doubt that, I'll still add the end of the joke:

… and Mitchell Baker will fire all of Mozilla's engine developers and use the money saved by that to give herself another multi-million dollar salary raise.

https://en.wikipedia.org/wiki/Mitchell_Baker#Negative_salary...

Gecko engine looks pretty healthy to me overall. And WebGPU in particular is the least of a concern, given that Firefox's implementation is based on wgpu [1], which has great community and a lot of users within and outside of Rust ecosystem. I'm confident Firefox can ship it soon (tm).

[1] https://github.com/gfx-rs/wgpu

At least Edge does offer additional browser features for OS integration and extended developer tools.