Bug 729307 - Add full-screen-api.exit-on-deactivate pref. r=dao

browser/base/content/browser.js

@@ -4043,7 +4043,9 @@ var FullScreen = {
     gBrowser.tabContainer.addEventListener("TabSelect", this.exitDomFullScreen);
 
     // Exit DOM full-screen mode when the browser window loses focus (ALT+TAB, etc).
-    window.addEventListener("deactivate", this.exitDomFullScreen, true);
+    if (gPrefService.getBoolPref("full-screen-api.exit-on-deactivate")) {
+      window.addEventListener("deactivate", this.exitDomFullScreen, true);
+    }
 
     // Cancel any "hide the toolbar" animation which is in progress, and make
     // the toolbar hide immediately.

modules/libpref/src/init/all.js

@@ -3409,6 +3409,7 @@ pref("full-screen-api.enabled", false);
 pref("full-screen-api.allow-trusted-requests-only", true);
 pref("full-screen-api.key-input-restricted", true);
 pref("full-screen-api.warning.enabled", true);
+pref("full-screen-api.exit-on-deactivate", true);
 
 // Time limit, in milliseconds, for nsEventStateManager::IsHandlingUserInput().
 // Used to detect long running handlers of user-generated events.