`sound` component not loading audio in Firefox

Description:

Using the current A-Frame master, when trying to auto play audio with the sound component using autoplay: true, either the loading screen times out and the audio doesn't play, or the loading screen skips and the audio doesn't play.

This seems to be affecting Firefox on pretty much every platform I've tested. In Chrome, everything loads almost immediately and the audio plays as expected.

In Firefox, console says:

components:sound:warn Sound not loaded yet. It will be played once it finished loading 

The audio never plays.

If I try document.querySelector('audio'), play(), it will play, but it appears the sound component gets hung up.

document.querySelector('[sound]').components.sound.playSound() throws the same console message.

I processed the audio with ffmpeg in the second demo, to make sure it wasn't an encoding issue, but no dice.

• A-Frame Version: master 826e983d989312fe7cd75b9cc92e58b7a5cc195f
• Platform / Device: Firefox on Windows/Mac/Android...
• Reproducible Code Snippet or URL:

https://bunker-bake.glitch.me
https://spiral-lipstick.glitch.me

Start by reproducing the issue in Firefox using the two demos at bunker-bake.glitch.me and spiral-lipstick.glitch.me, then trace the A-Frame sound component's loading path. Compare its behavior with direct HTMLAudioElement playback and verify that autoplay audio loads and plays in Firefox without the reported warning.