Bug 1133012 - Disable tab mirroring on RELEASE r=snorp

mobile/android/app/mobile.js

@@ -280,12 +280,14 @@ pref("browser.search.noCurrentEngine", true);
 
 // Control media casting & mirroring features
 pref("browser.casting.enabled", true);
-pref("browser.mirroring.enabled", true);
 #ifdef RELEASE_BUILD
 // Roku does not yet support mirroring in production
 pref("browser.mirroring.enabled.roku", false);
+// Chromecast mirroring is broken (bug 1131084)
+pref("browser.mirroring.enabled", false);
 #else
 pref("browser.mirroring.enabled.roku", true);
+pref("browser.mirroring.enabled", true);
 #endif
 
 // Enable sparse localization by setting a few package locale overrides