Update user.js

* autoplay option "Prompt" was removed in FF66
source: https://hg.mozilla.org/integration/autoland/rev/2e48b6769911

user.js

@@ -1,7 +1,7 @@
 /******
 * name: ghacks user.js
-* date: 27 March 2019
-* version 66-beta: The Power of Pants
+* date: 15 April 2019
+* version 66: The Power of Pants
 *   "The power of pants is a curious thing. Make a one man weep, make another man sing"
 * authors: v52+ github | v51- www.ghacks.net
 * url: https://github.com/ghacksuserjs/ghacks-user.js
@@ -1080,7 +1080,7 @@ user_pref("dom.imagecapture.enabled", false); // [DEFAULT: false]
  * [1] https://developer.mozilla.org/docs/Web/API/OffscreenCanvas ***/
 user_pref("gfx.offscreencanvas.enabled", false); // [DEFAULT: false]
 /* 2030: disable autoplay of HTML5 media [FF63+]
- * 0=Allowed, 1=Blocked, 2=Prompt
+ * 0=Allowed, 1=Blocked (2=Prompt - removed in FF66)
  * [NOTE] You can set exceptions under site permissions
  * [SETTING] Privacy & Security>Permissions>Block websites from automatically playing sound ***/
 user_pref("media.autoplay.default", 1);
@@ -1321,6 +1321,7 @@ user_pref("permissions.manager.defaultsUrl", "");
 user_pref("webchannel.allowObject.urlWhitelist", "");
 /* 2618: disable exposure of system colors to CSS or canvas [FF44+]
  * [NOTE] See second listed bug: may cause black on black for elements with undefined colors
+ * [SETUP-CHROME] Might affect CSS in themes and extensions
  * [1] https://bugzilla.mozilla.org/buglist.cgi?bug_id=232227,1330876 ***/
 user_pref("ui.use_standins_for_native_colors", true); // [HIDDEN PREF]
 /* 2619: enforce Punycode for Internationalized Domain Names to eliminate possible spoofing
@@ -1367,7 +1368,8 @@ user_pref("browser.download.forbid_open_with", true);
 
 /** EXTENSIONS ***/
 /* 2660: lock down allowed extension directories
- * [SETUP-CHROME] This will break extensions that do not use the default XPI directories
+ * [SETUP-CHROME] This will break extensions, language packs, themes and any other XPI files which are
+ * installed outside of profile directories (see GitHub issue #674 for an issue with language packs in Linux)
  * [1] https://mike.kaply.com/2012/02/21/understanding-add-on-scopes/
  * [1] archived: https://archive.is/DYjAM ***/
 user_pref("extensions.enabledScopes", 1); // [HIDDEN PREF]
@@ -1620,6 +1622,8 @@ user_pref("privacy.firstparty.isolate.restrict_opener_access", true); // [DEFAUL
       FF65: pointerEvent.pointerid (1492766)
  ** 1485266 - disable exposure of system colors to CSS or canvas (see 2618) (FF67+)
  ** 1407366 - enable inner window letterboxing (see 4504) (FF67+)
+ ** 1540726 - enforce "light" with prefers-color-scheme (FF67+)
+        [1] https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme
 ***/
 user_pref("_user.js.parrot", "4500 syntax error: the parrot's popped 'is clogs");
 /* 4501: enable privacy.resistFingerprinting [FF41+]