Safari mute button appears in Firefox

[microbit-carlos]

Describe the bug As briefly mentioned in:

• https://github.com/microsoft/pxt-microbit/pull/5277#issuecomment-2100356419

The mute button that had to be added to safari has started appearing (unnecessarily) in Firefox as well.

To Reproduce Steps to reproduce the behavior:

1. Go to https://makecode.microbit.org/beta on Firefox
2. Create a project and add a block to play a sound
3. The unmute button should be on top of the simualtor

Expected behavior No mute button to be rendered and the simulator to play sound automaticallu.

Screenshots

micro:bit version (please complete the following information): N/A

Desktop (please complete the following information): macOS 13 firefox v126

Smartphone (please complete the following information): N/A

Additional context N/A