diff --git a/browser/app/profile/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/install.rdf.in b/browser/app/profile/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/install.rdf.in
index 3335403f419..f8eccb46554 100644
--- a/browser/app/profile/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/install.rdf.in
+++ b/browser/app/profile/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}/install.rdf.in
@@ -23,20 +23,13 @@
     <em:name>Default</em:name>
     <em:description>The default theme.</em:description>
 
-    <!-- EXTENSION AUTHORS!
-         DO NOT COPY THIS PROPERTY INTO YOUR INSTALL RDF FILES
-         It will cause users not to be informed of incompatibilities 
-         with your extension when they are updated with Software Update
-         and your extension will become unavailable to them!
-         -->
-    <em:appManaged>true</em:appManaged>
-
-    <em:locked>true</em:locked>
-
     <!-- Front End Integration Hooks (used by Theme Manager)-->
     <em:creator>Mozilla</em:creator>
     <em:contributor>Mozilla Contributors</em:contributor>
 
+    <!-- Allow lightweight themes to apply to this theme -->
+    <em:skinnable>true</em:skinnable>
+
     <em:internalName>classic/1.0</em:internalName>
   </Description>      
 
diff --git a/toolkit/mozapps/extensions/test/addons/test_theme/install.rdf b/toolkit/mozapps/extensions/test/addons/test_theme/install.rdf
index 6ab808a018d..e1a37d0a49c 100644
--- a/toolkit/mozapps/extensions/test/addons/test_theme/install.rdf
+++ b/toolkit/mozapps/extensions/test/addons/test_theme/install.rdf
@@ -20,5 +20,7 @@
       </Description>
     </em:targetApplication>
 
+    <em:skinnable>true</em:skinnable>
+
   </Description>
 </RDF>
diff --git a/toolkit/mozapps/extensions/test/xpcshell/head_addons.js b/toolkit/mozapps/extensions/test/xpcshell/head_addons.js
index 65c3fce3f12..356f9ab5938 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/head_addons.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/head_addons.js
@@ -355,7 +355,7 @@ function writeInstallRDFToDir(aData, aDir) {
   rdf += '<Description about="urn:mozilla:install-manifest">\n';
 
   ["id", "version", "type", "internalName", "updateURL", "updateKey",
-   "optionsURL", "aboutURL", "iconURL"].forEach(function(aProp) {
+   "optionsURL", "aboutURL", "iconURL", "skinnable"].forEach(function(aProp) {
     if (aProp in aData)
       rdf += "<em:" + aProp + ">" + escapeXML(aData[aProp]) + "</em:" + aProp + ">\n";
   });
diff --git a/toolkit/mozapps/extensions/test/xpcshell/test_theme.js b/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
index 3dfe47d7ffd..647dfda940c 100644
--- a/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_theme.js
@@ -42,6 +42,7 @@ function run_test() {
     version: "1.0",
     name: "Test 1",
     type: 4,
+    skinnable: true,
     internalName: "theme1/1.0",
     targetApplications: [{
       id: "xpcshell@tests.mozilla.org",
@@ -56,6 +57,7 @@ function run_test() {
     id: "theme2@tests.mozilla.org",
     version: "1.0",
     name: "Test 1",
+    skinnable: false,
     internalName: "theme2/1.0",
     targetApplications: [{
       id: "xpcshell@tests.mozilla.org",
@@ -88,12 +90,18 @@ function run_test() {
   AddonManager.addAddonListener(AddonListener);
   AddonManager.addInstallListener(InstallListener);
 
-  AddonManager.getAddonsByIDs(["theme1@tests.mozilla.org",
-                               "theme2@tests.mozilla.org"], function([t1, t2]) {
+  AddonManager.getAddonsByIDs(["default@tests.mozilla.org",
+                               "theme1@tests.mozilla.org",
+                               "theme2@tests.mozilla.org"],
+                               function([d, t1, t2]) {
+    do_check_neq(d, null);
+    do_check_false(d.skinnable);
+
     do_check_neq(t1, null);
     do_check_false(t1.userDisabled);
     do_check_false(t1.appDisabled);
     do_check_true(t1.isActive);
+    do_check_true(t1.skinnable);
     do_check_eq(t1.screenshots.length, 0);
     do_check_true(isThemeInAddonsList(profileDir, t1.id));
     do_check_false(hasFlag(t1.permissions, AddonManager.PERM_CAN_DISABLE));
@@ -103,6 +111,7 @@ function run_test() {
     do_check_true(t2.userDisabled);
     do_check_false(t2.appDisabled);
     do_check_false(t2.isActive);
+    do_check_false(t2.skinnable);
     do_check_eq(t2.screenshots.length, 0);
     do_check_false(isThemeInAddonsList(profileDir, t2.id));
     do_check_false(hasFlag(t2.permissions, AddonManager.PERM_CAN_DISABLE));
@@ -643,6 +652,7 @@ function run_test_11() {
     do_check_eq(install.version, "1.0");
     do_check_eq(install.name, "Test Theme 1");
     do_check_eq(install.state, AddonManager.STATE_DOWNLOADED);
+    do_check_true(install.addon.skinnable, true);
 
     prepare_test({
       "theme1@tests.mozilla.org": [
@@ -665,6 +675,7 @@ function check_test_11() {
     preview.append("preview.png");
     do_check_eq(t1.screenshots.length, 1);
     do_check_eq(t1.screenshots[0], NetUtil.newURI(preview).spec);
+    do_check_true(t1.skinnable);
     do_check_false(gLWThemeChanged);
 
     run_test_12();