Bug 1540856: Part 2 - Fix broken default theme check. r=aswan

Differential Revision: https://phabricator.services.mozilla.com/D25678

--HG--
extra : rebase_source : f41bbcd42368cad241e787901a7fbdecfe50d345
extra : histedit_source : ca4f073a4c805b6eae4c33be27e2548dc50cada1

browser/components/BrowserGlue.jsm

@@ -304,7 +304,7 @@ let ACTORS = {
 
   // Until bug 1450626 and bug 1488384 are fixed, skip the blank window when
   // using a non-default theme.
-  if (Services.prefs.getCharPref("lightweightThemes.selectedThemeID", "") !=
+  if (Services.prefs.getCharPref("extensions.activeThemeID", "") !=
         "default-theme@mozilla.org")
     return;
 

toolkit/mozapps/extensions/internal/XPIDatabase.jsm

@@ -1624,6 +1624,8 @@ this.XPIDatabase = {
     if (aType !== "theme")
       return;
 
+    Services.prefs.setCharPref("extensions.activeThemeID", aId || DEFAULT_THEME_ID);
+
     let enableTheme;
 
     let addons = this.getAddonsByType("theme");