Bug 1164178 - Use an empty value by default for lightweightThemes.selectedThemeID;r=dao

browser/app/profile/firefox.js

@@ -1332,6 +1332,8 @@ pref("services.sync.prefs.sync.xpinstall.whitelist.required", true);
 #ifdef MOZ_DEV_EDITION
 sticky_pref("lightweightThemes.selectedThemeID", "firefox-devedition@mozilla.org");
 sticky_pref("browser.devedition.theme.enabled", true);
+#else
+sticky_pref("lightweightThemes.selectedThemeID", "");
 #endif
 
 // Developer edition promo preferences

browser/components/customizableui/test/browser_1007336_lwthemes_in_customize_mode.js

@@ -51,7 +51,7 @@ add_task(function () {
 
   let defaultTheme = header.nextSibling;
   defaultTheme.doCommand();
-  is(Services.prefs.prefHasUserValue("lightweightThemes.selectedThemeID"), false, "No lwtheme should be selected");
+  is(Services.prefs.getCharPref("lightweightThemes.selectedThemeID"), "", "No lwtheme should be selected");
 });
 
 add_task(function asyncCleanup() {

toolkit/mozapps/extensions/LightweightThemeManager.jsm

@@ -302,7 +302,7 @@ this.LightweightThemeManager = {
     if (aData)
       _prefs.setCharPref("selectedThemeID", aData.id);
     else
-      _prefs.deleteBranch("selectedThemeID");
+      _prefs.setCharPref("selectedThemeID", "");
 
     _notifyWindows(aData);
     Services.obs.notifyObservers(null, "lightweight-theme-changed", null);