diff --git a/toolkit/mozapps/extensions/AddonManager.jsm b/toolkit/mozapps/extensions/AddonManager.jsm
index 8f5383f70f47..ff998604bc2a 100644
--- a/toolkit/mozapps/extensions/AddonManager.jsm
+++ b/toolkit/mozapps/extensions/AddonManager.jsm
@@ -274,6 +274,10 @@ var AddonManagerInternal = {
     if (!Services.prefs.getBoolPref(PREF_EM_UPDATE_ENABLED))
       return;
 
+    let scope = {};
+    Components.utils.import("resource://gre/modules/LightweightThemeManager.jsm", scope);
+    scope.LightweightThemeManager.updateCurrentTheme();
+
     this.getAddonsByTypes(null, function getAddonsCallback(addons) {
       addons.forEach(function BUC_forEachCallback(addon) {
         if (addon.permissions & AddonManager.PERM_CAN_UPGRADE) {
diff --git a/toolkit/mozapps/extensions/LightweightThemeManager.jsm b/toolkit/mozapps/extensions/LightweightThemeManager.jsm
index 6353e5b6677b..0bdc1e1fe6c3 100644
--- a/toolkit/mozapps/extensions/LightweightThemeManager.jsm
+++ b/toolkit/mozapps/extensions/LightweightThemeManager.jsm
@@ -516,24 +516,24 @@ function _setCurrentTheme(aData, aLocal) {
 
   if (aData) {
     let theme = LightweightThemeManager.getUsedTheme(aData.id);
-    // TODO detect if it is an install and act accordingly
-    if (!theme) {
+    let isInstall = !theme || theme.version != aData.version;
+    if (isInstall) {
+      var oldWrapper = theme ? new AddonWrapper(theme) : null;
       var wrapper = new AddonWrapper(aData);
       AddonManagerPrivate.callInstallListeners("onExternalInstall", null,
-                                               wrapper, null, false);
+                                               wrapper, oldWrapper, false);
       AddonManagerPrivate.callAddonListeners("onInstalling", wrapper, false);
     }
-    let current = LightweightThemeManager.currentTheme;
-    if (!current || current.id != aData.id) {
-      let usedThemes = _usedThemesExceptId(aData.id);
-      if (current)
-        usedThemes.splice(1, 0, aData);
-      else
-        usedThemes.unshift(aData);
-      _updateUsedThemes(usedThemes);
-    }
 
-    if (!theme)
+    let current = LightweightThemeManager.currentTheme;
+    let usedThemes = _usedThemesExceptId(aData.id);
+    if (current && current.id != aData.id)
+      usedThemes.splice(1, 0, aData);
+    else
+      usedThemes.unshift(aData);
+    _updateUsedThemes(usedThemes);
+
+    if (isInstall)
        AddonManagerPrivate.callAddonListeners("onInstalled", wrapper);
   }
 
diff --git a/toolkit/mozapps/extensions/test/xpcshell/test_theme.js b/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
index 4a3f52924a6a..e561fbee9c25 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
@@ -662,7 +662,7 @@ function run_test_13() {
       do_check_eq(install.version, "1.0");
       do_check_eq(install.name, "Test Theme 1");
       do_check_eq(install.state, AddonManager.STATE_DOWNLOADED);
-  
+
       prepare_test({
         "theme1@tests.mozilla.org": [
           "onInstalling",
diff --git a/toolkit/mozapps/extensions/test/xpcshell/test_update.js b/toolkit/mozapps/extensions/test/xpcshell/test_update.js
index 2840ab1247cc..698623ce0e6d 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/test_update.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_update.js
@@ -7,6 +7,8 @@
 // The test extension uses an insecure update url.
 Services.prefs.setBoolPref("extensions.checkUpdateSecurity", false);
 
+Components.utils.import("resource://gre/modules/LightweightThemeManager.jsm");
+
 do_load_httpd_js();
 var testserver;
 var profileDir;
@@ -229,6 +231,76 @@ function check_test_4(install) {
     a1.uninstall();
     restartManager(0);
 
+    run_test_5();
+  });
+}
+
+// Test that background update checks work for lightweight themes
+function run_test_5() {
+  LightweightThemeManager.currentTheme = {
+    id: "1",
+    version: "1",
+    name: "Test LW Theme",
+    description: "A test theme",
+    author: "Mozilla",
+    homepageURL: "http://localhost:4444/data/index.html",
+    headerURL: "http://localhost:4444/data/header.png",
+    footerURL: "http://localhost:4444/data/footer.png",
+    previewURL: "http://localhost:4444/data/preview.png",
+    iconURL: "http://localhost:4444/data/icon.png",
+    updateURL: "http://localhost:4444/data/lwtheme.js"
+  };
+
+  // XXX The lightweight theme manager strips non-https updateURLs so hack it
+  // back in.
+  let themes = JSON.parse(Services.prefs.getCharPref("lightweightThemes.usedThemes"));
+  do_check_eq(themes.length, 1);
+  themes[0].updateURL = "http://localhost:4444/data/lwtheme.js";
+  Services.prefs.setCharPref("lightweightThemes.usedThemes", JSON.stringify(themes));
+
+  testserver.registerPathHandler("/data/lwtheme.js", function(request, response) {
+    response.write(JSON.stringify({
+      id: "1",
+      version: "2",
+      name: "Updated Theme",
+      description: "A test theme",
+      author: "Mozilla",
+      homepageURL: "http://localhost:4444/data/index2.html",
+      headerURL: "http://localhost:4444/data/header.png",
+      footerURL: "http://localhost:4444/data/footer.png",
+      previewURL: "http://localhost:4444/data/preview.png",
+      iconURL: "http://localhost:4444/data/icon2.png",
+      updateURL: "http://localhost:4444/data/lwtheme.js"
+    }));
+  });
+
+  AddonManager.getAddon("1@personas.mozilla.org", function(p1) {
+    do_check_neq(p1, null);
+    do_check_eq(p1.version, "1");
+    do_check_eq(p1.name, "Test LW Theme");
+    do_check_true(p1.isActive);
+
+    prepare_test({
+      "1@personas.mozilla.org": [
+        ["onInstalling", false],
+        "onInstalled"
+      ]
+    }, [
+      "onExternalInstall"
+    ], check_test_5);
+  
+    // Fake a timer event to cause a background update and wait for the magic to
+    // happen
+    gInternalManager.notify(null);
+  });
+}
+
+function check_test_5() {
+  AddonManager.getAddon("1@personas.mozilla.org", function(p1) {
+    do_check_neq(p1, null);
+    do_check_eq(p1.version, "2");
+    do_check_eq(p1.name, "Updated Theme");
+
     end_test();
   });
 }