--- a/toolkit/components/extensions/ExtensionPreferencesManager.jsm
+++ b/toolkit/components/extensions/ExtensionPreferencesManager.jsm
@@ -337,17 +337,21 @@ this.ExtensionPreferencesManager = {
    *
    * @returns {Promise}
    *          Resolves to the level of control of the extension over the setting.
    */
   async getLevelOfControl(extension, name, storeType = STORE_TYPE) {
     // This could be called for a setting that isn't defined to the PreferencesManager,
     // in which case we simply defer to the SettingsStore.
     if (storeType === STORE_TYPE) {
-      for (let prefName of settingsMap.get(name).prefNames) {
+      let setting = settingsMap.get(name);
+      if (!setting) {
+        return "not_controllable";
+      }
+      for (let prefName of setting.prefNames) {
         if (Preferences.locked(prefName)) {
           return "not_controllable";
         }
       }
     }
     await ExtensionSettingsStore.initialize();
     return ExtensionSettingsStore.getLevelOfControl(extension, storeType, name);
   },

new file mode 100644
--- /dev/null
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_browserSettings_homepage.js
@@ -0,0 +1,29 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+add_task(async function test_homepage_get_without_set() {
+  async function background() {
+    let homepage = await browser.browserSettings.homepageOverride.get({});
+    browser.test.sendMessage("homepage", homepage);
+  }
+
+  let extension = ExtensionTestUtils.loadExtension({
+    background,
+    manifest: {
+      permissions: ["browserSettings"],
+    },
+  });
+
+  let defaultHomepage = Services.prefs.getComplexValue(
+    "browser.startup.homepage", Ci.nsIPrefLocalizedString).data;
+
+  await extension.startup();
+  let homepage = await extension.awaitMessage("homepage");
+  equal(homepage.value, defaultHomepage,
+        "The homepageOverride setting has the expected value.");
+  equal(homepage.levelOfControl, "not_controllable",
+        "The homepageOverride setting has the expected levelOfControl.");
+
+  await extension.unload();
+});

--- a/toolkit/components/extensions/test/xpcshell/xpcshell-common.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell-common.ini
@@ -9,16 +9,18 @@
 skip-if = os == "android" # Android does not use Places for history.
 [test_ext_background_private_browsing.js]
 [test_ext_background_runtime_connect_params.js]
 [test_ext_background_sub_windows.js]
 [test_ext_background_telemetry.js]
 [test_ext_background_window_properties.js]
 skip-if = os == "android"
 [test_ext_browserSettings.js]
+[test_ext_browserSettings_homepage.js]
+skip-if = os == "android"
 [test_ext_contextual_identities.js]
 skip-if = os == "android" # Containers are not exposed to android.
 [test_ext_debugging_utils.js]
 [test_ext_downloads.js]
 [test_ext_downloads_download.js]
 skip-if = os == "android"
 [test_ext_downloads_misc.js]
 skip-if = os == "android" || (os=='linux' && bits==32) # linux32: bug 1324870