But DeepSpeech has already been trained with millions of data samples!

I'd feel way better about it if they went for a slightly worse DeepSpeech based implementation, but kept it working in the free software spirit they have been known about for many years.

Also, for desktop devices inference on DeepSpeech is cheap enough, so they could even go the extra mile and work on some Wasm magic to get offline recognition.

That's the kind of work I'd expect from Mozilla! Not wiring up your data collection to the Google Cloud APIs and call it a day! I'm genuinely disappointed with them...