Bug 1512283 - Turn off doorhanger in Nightly. r=cpearce

Now We decide to ship block-autoplay without doorhanger, so we would turn the pref off in Nightly.

Differential Revision: https://phabricator.services.mozilla.com/D13853

--HG--
extra : moz-landing-system : lando

browser/app/profile/firefox.js

@@ -1473,9 +1473,9 @@ pref("media.gmp-widevinecdm.enabled", true);
 // Switch block autoplay logic to v2, and enable UI.
 pref("media.autoplay.enabled.user-gestures-needed", true);
 // Allow asking for permission to autoplay to appear in UI.
-pref("media.autoplay.ask-permission", true);
+pref("media.autoplay.ask-permission", false);
 // Set Firefox to block autoplay, asking for permission by default.
-pref("media.autoplay.default", 2); // 0=Allowed, 1=Blocked, 2=Prompt
+pref("media.autoplay.default", 1); // 0=Allowed, 1=Blocked, 2=Prompt
 #else
 pref("media.autoplay.default", 0); // 0=Allowed, 1=Blocked, 2=Prompt
 pref("media.autoplay.enabled.user-gestures-needed", false);