Decide on autoplay policy and lock it down [bugzilla 1812190]

code so you know what is being tested

harden/lock prefs u guys

• about:preferences#privacy > permissions > autoplay > settings > default for all websites
  • this is media.autoplay.default

there are also other autoplay prefs, such as making things sticky or per element (user)

/* disable autoplay of HTML5 media if you interacted with the site [FF78+]
 * 0=sticky (default), 1=transient, 2=user
 * Firefox's Autoplay Policy Documentation (PDF) is linked below via SUMO
 * [NOTE] If you have trouble with some video sites, then add an exception (2030)
 * [1] https://support.mozilla.org/questions/1293231 ***/
user_pref("media.autoplay.blocking_policy", 2);

[1] https://developer.mozilla.org/en-US/docs/Web/API/Navigator/getAutoplayPolicy

[2] https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/112