diff -up comm-release/mail/app/profile/all-thunderbird.js.addons comm-release/mail/app/profile/all-thunderbird.js
--- comm-release/mail/app/profile/all-thunderbird.js.addons	2011-11-15 10:36:03.868551158 +0100
+++ comm-release/mail/app/profile/all-thunderbird.js	2011-11-15 10:36:20.555397903 +0100
@@ -138,7 +138,7 @@ pref("extensions.update.autoUpdateDefaul
 // Disable add-ons installed into the shared user and shared system areas by
 // default. This does not include the application directory. See the SCOPE
 // constants in AddonManager.jsm for values to use here
-pref("extensions.autoDisableScopes", 15);
+pref("extensions.autoDisableScopes", 0);
 
 // Preferences for AMO integration
 pref("extensions.getAddons.cache.enabled", true);
diff -up comm-release/mozilla/toolkit/mozapps/extensions/XPIProvider.jsm.addons comm-release/mozilla/toolkit/mozapps/extensions/XPIProvider.jsm
--- comm-release/mozilla/toolkit/mozapps/extensions/XPIProvider.jsm.addons	2011-11-15 11:15:06.518905245 +0100
+++ comm-release/mozilla/toolkit/mozapps/extensions/XPIProvider.jsm	2011-11-15 11:15:40.399934236 +0100
@@ -1591,8 +1591,8 @@ var XPIProvider = {
       this.showUpgradeUI();
       flushCaches = true;
     }
-    else if (aAppChanged === undefined) {
-      // For new profiles we will never need to show the add-on selection UI
+    else {
+      // For all profiles we will never need to show the add-on selection UI
       Services.prefs.setBoolPref(PREF_SHOWN_SELECTION_UI, true);
     }