Turns out, in Firefox mobile, the email submission block isn't present.

I had to open Chrome Mobile to see it.

I hope this, err, 'oversight' isn't indicative of the quality of using Mozilla products.

Yep. You might need to disable Adblock to have it appear.

I was still hoping for something more than a simple email waitlist signup however. But I didn’t find anything obvious hidden in the page that would allow immediate signup

I had to disable uBlock Origin for that to show up.