Ooops, my big bad, I'll add a memo regarding this!

I couldn't make it work in Firefox yet: FF has a limited support for SpeechRecognition, that is enabled only via a flag. Even then it didn't work with my example. I'll dig into it further!

Meanwhile, to lessen the disappointment:

You can try this example in desktop/android chrome

OR

In FF open about:config and turn on these flags media.webspeech.recognition.enable media.webspeech.recognition.force_enable

(remember to turn em off after)

And then try official MDN example for Speech Recognition: https://mdn.github.io/web-speech-api/speech-color-changer/

Sorry for the trouble!