[QA] Play button functionality is not working on Firefox

### Description

Play button functionality is not working

### Reproduction Steps

Test Case - [1.5.5 amp-audio/play]

Playground Link - https://playground.amp.dev/?url=https%3A%2F%2Fpreview.amp.dev%2Fdocumentation%2Fexamples%2Fcomponents%2Famp-audio&format=websites

Steps:
1) Launch Playground link.
2) Click on play button on any of the audio link.

Observed : Play button is not functioning.
https://recall.googleplex.com/projects/effc1364-8f41-414e-b99a-5eabccae10b7/sessions/0f5ff459-b2b5-4206-ac0e-1ff555ab8aec

Expected : Play button should work fine.

### Relevant Logs

_No response_

### Browser(s) Affected

Firefox

### OS(s) Affected

NA

### Device(s) Affected

NA

### AMP Version Affected

2308112021001

Start with the amp-audio/play test case and reproduce the issue in Firefox using the linked AMP Playground amp-audio example. Trace the play button behavior and compare it with a working browser; done means audio starts when any audio link's play button is clicked in Firefox.

Written by the indexing model from the issue text.