From
https://www.ghacks.net/2019/06/18/block-autoplaying-video-and-audio-in-firefox-69-natively/
Starting in Firefox 69, about:config parameters changed in regards to
Firefox's autoplay blocking behavior.
media.autoplay.default
• Value 5: Block audio and video
• Value 1: Block audio
• Value 0: allow
media.autoplay.block-webaudio
• Value True: Block
• Value False: Allow
media.autoplay.enabled.user-gestures-needed
• Value True: Require user interaction
• Value False: Don't require user interaction
Removed:
• media.autoplay.enabled
• media.autoplay.allow-muted