diff --git a/toolkit/components/webextensions/ExtensionStorage.jsm b/toolkit/components/webextensions/ExtensionStorage.jsm
index 0b0ffb0003..728cba728c 100644
--- a/toolkit/components/webextensions/ExtensionStorage.jsm
+++ b/toolkit/components/webextensions/ExtensionStorage.jsm
@@ -197,6 +197,19 @@ this.ExtensionStorage = {
     });
   },
 
+  getManaged(keys) {
+    // Managed storage is populated by enterprise policy, which this UXP
+    // branch does not implement. Return the requested defaults, matching the
+    // WebExtension storage contract for an empty managed area.
+    if (keys === null || keys === undefined) {
+      return Promise.resolve({});
+    }
+    if (typeof(keys) == "object" && !Array.isArray(keys)) {
+      return Promise.resolve(Object.assign({}, keys));
+    }
+    return Promise.resolve({});
+  },
+
   addOnChangedListener(extensionId, listener) {
     let listeners = this.listeners.get(extensionId) || new Set();
     listeners.add(listener);
diff --git a/toolkit/components/webextensions/ext-c-storage.js b/toolkit/components/webextensions/ext-c-storage.js
index e8d53058f6..34abcd2254 100644
--- a/toolkit/components/webextensions/ext-c-storage.js
+++ b/toolkit/components/webextensions/ext-c-storage.js
@@ -41,6 +41,27 @@ function storageApiFactory(context) {
         },
       },
 
+      managed: {
+        get: function(keys) {
+          keys = sanitize(keys);
+          return context.childManager.callParentAsyncFunction("storage.managed.get", [
+            keys,
+          ]);
+        },
+        set: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+        remove: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+        clear: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+      },
+
       sync: {
         get: function(keys) {
           keys = sanitize(keys);
diff --git a/toolkit/components/webextensions/ext-storage.js b/toolkit/components/webextensions/ext-storage.js
index b1e22c46c0..4bc5168fd1 100644
--- a/toolkit/components/webextensions/ext-storage.js
+++ b/toolkit/components/webextensions/ext-storage.js
@@ -29,6 +29,27 @@ function storageApiFactory(context) {
         },
       },
 
+      // UXP has no enterprise managed-storage backend. Expose the namespace
+      // as an empty, read-only area so extensions can feature-detect it and
+      // continue using their defaults.
+      managed: {
+        get: function(spec) {
+          return ExtensionStorage.getManaged(spec);
+        },
+        set: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+        remove: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+        clear: function() {
+          throw new context.cloneScope.Error(
+            "storage.managed is read-only");
+        },
+      },
+
       onChanged: new EventManager(context, "storage.onChanged", fire => {
         let listenerLocal = changes => {
           fire(changes, "local");
diff --git a/toolkit/components/webextensions/schemas/manifest.json b/toolkit/components/webextensions/schemas/manifest.json
index 2b69e72fd4..7212db4781 100644
--- a/toolkit/components/webextensions/schemas/manifest.json
+++ b/toolkit/components/webextensions/schemas/manifest.json
@@ -183,6 +183,29 @@
             "optional": true
           },
 
+          "optional_permissions": {
+            "type": "array",
+            "items": {
+              "choices": [
+                { "$ref": "Permission" },
+                {
+                  "type": "string",
+                  "deprecated": "Unknown optional permission ${value}"
+                }
+              ]
+            },
+            "optional": true
+          },
+
+          "user_scripts": {
+            "type": "object",
+            "optional": true,
+            "properties": {
+              "api_script": { "$ref": "ExtensionURL" }
+            },
+            "additionalProperties": { "$ref": "UnrecognizedProperty" }
+          },
+
           "web_accessible_resources": {
             "type": "array",
             "items": { "type": "string" },
@@ -218,6 +241,7 @@
             "enum": [
               "alarms",
               "clipboardWrite",
+              "contextualIdentities",
               "dns",
               "idle",
               "menus",
@@ -387,8 +411,7 @@
       },
       {
         "id": "PersistentBackgroundProperty",
-        "type": "boolean",
-        "deprecated": "Event pages are not currently supported. This will run as a persistent background page."
+        "type": "boolean"
       }
     ]
   }
diff --git a/toolkit/components/webextensions/schemas/storage.json b/toolkit/components/webextensions/schemas/storage.json
index a54a209424..35e3931902 100644
--- a/toolkit/components/webextensions/schemas/storage.json
+++ b/toolkit/components/webextensions/schemas/storage.json
@@ -220,7 +220,6 @@
         }
       },
       "managed": {
-        "unsupported": true,
         "$ref": "StorageArea",
         "description": "Items in the <code>managed</code> storage area are set by the domain administrator, and are read-only for the extension; trying to modify this namespace results in an error."
       }