This extension is trying to provide some useful functionality in the hopes that Mozilla gets more data for https://commonvoice.mozilla.org
I'd at least consider recording your voice, especially if you're a non-native English speaker, like myself, have an accent etc.
It took many years for free software to start to take on the smartphone segment, with previous efforts, (including by Mozilla), failing and only now PinePhone & Librem 5 giving it another go, but unless you're a super hardcore enthusiast, you carry an iPhone/Android today.
I see this as a way to push back on the likes of Amazon, Google and Apple with this. If regular Firefox users are able to use an on-device, privacy respecting voice assistance and other open-source projects can use Mozilla's tools and datasets to build compelling competitors to Alexa, I'd see that as proof that free software is able to address new, emerging markets too.