diff --git a/browser/components/extensions/test/browser/browser-common.ini b/browser/components/extensions/test/browser/browser-common.ini
index 8a8e9d1cd8af..f4cc5c9d9744 100644
--- a/browser/components/extensions/test/browser/browser-common.ini
+++ b/browser/components/extensions/test/browser/browser-common.ini
@@ -118,7 +118,6 @@ support-files =
 [browser_ext_tabs_zoom.js]
 [browser_ext_tabs_update_url.js]
 [browser_ext_themes_icons.js]
-[browser_ext_themes_validation.js]
 [browser_ext_topwindowid.js]
 [browser_ext_url_overrides_newtab.js]
 [browser_ext_url_overrides_home.js]
diff --git a/browser/components/extensions/test/browser/browser_ext_themes_validation.js b/browser/components/extensions/test/browser/browser_ext_themes_validation.js
deleted file mode 100644
index 1c62aa8dcde9..000000000000
--- a/browser/components/extensions/test/browser/browser_ext_themes_validation.js
+++ /dev/null
@@ -1,56 +0,0 @@
-"use strict";
-
-add_task(function* setup() {
-  yield SpecialPowers.pushPrefEnv({
-    set: [["extensions.webextensions.themes.enabled", true]],
-  });
-});
-
-/**
- * Helper function for testing a theme with invalid properties.
- * @param {object} invalidProps The invalid properties to load the theme with.
- */
-function* testThemeWithInvalidProperties(invalidProps) {
-  let manifest = {
-    "theme": {},
-  };
-
-  invalidProps.forEach(prop => {
-    // Some properties require additional information:
-    switch (prop) {
-      case "background":
-        manifest[prop] = {"scripts": ["background.js"]};
-        break;
-      case "permissions":
-        manifest[prop] = ["tabs"];
-        break;
-      case "omnibox":
-        manifest[prop] = {"keyword": "test"};
-        break;
-      default:
-        manifest[prop] = {};
-    }
-  });
-
-  let extension = ExtensionTestUtils.loadExtension({manifest});
-
-  SimpleTest.waitForExplicitFinish();
-  let waitForConsole = new Promise(resolve => {
-    SimpleTest.monitorConsole(resolve, [{
-      message: /Reading manifest: Themes defined in the manifest may only contain static resources/,
-    }]);
-  });
-
-  yield Assert.rejects(extension.startup(), null, "Theme should fail to load if it contains invalid properties");
-
-  SimpleTest.endMonitorConsole();
-  yield waitForConsole;
-}
-
-add_task(function* test_that_theme_with_invalid_properties_fails_to_load() {
-  let invalidProps = ["page_action", "browser_action", "background", "permissions", "omnibox", "commands"];
-  for (let prop in invalidProps) {
-    yield testThemeWithInvalidProperties([prop]);
-  }
-  yield testThemeWithInvalidProperties(invalidProps);
-});
diff --git a/toolkit/components/extensions/test/xpcshell/test_ext_themes_supported_properties.js b/toolkit/components/extensions/test/xpcshell/test_ext_themes_supported_properties.js
deleted file mode 100644
index 93a7319b7f0a..000000000000
--- a/toolkit/components/extensions/test/xpcshell/test_ext_themes_supported_properties.js
+++ /dev/null
@@ -1,71 +0,0 @@
-/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
-/* vim: set sts=2 sw=2 et tw=80: */
-"use strict";
-
-Cu.import("resource://gre/modules/ExtensionUtils.jsm");
-Cu.import("resource://gre/modules/Schemas.jsm");
-
-const {
-  validateThemeManifest,
-} = ExtensionUtils;
-
-const BASE_SCHEMA_URL = "chrome://extensions/content/schemas/manifest.json";
-const CATEGORY_EXTENSION_SCHEMAS = "webextension-schemas";
-
-const baseManifestProperties = [
-  "manifest_version",
-  "minimum_chrome_version",
-  "applications",
-  "browser_specific_settings",
-  "name",
-  "short_name",
-  "description",
-  "author",
-  "version",
-  "homepage_url",
-  "icons",
-  "incognito",
-  "background",
-  "options_ui",
-  "content_scripts",
-  "permissions",
-  "web_accessible_resources",
-  "developer",
-];
-
-function* getAdditionalInvalidManifestProperties() {
-  let invalidProperties = [];
-  yield Schemas.load(BASE_SCHEMA_URL);
-  for (let [name, url] of XPCOMUtils.enumerateCategoryEntries(CATEGORY_EXTENSION_SCHEMAS)) {
-    if (name !== "theme") {
-      yield Schemas.load(url);
-      let types = Schemas.schemaJSON.get(url)[0].types;
-      types.forEach(type => {
-        if (type.$extend == "WebExtensionManifest") {
-          let properties = Object.getOwnPropertyNames(type.properties);
-          invalidProperties.push(...properties);
-        }
-      });
-    }
-  }
-
-  // Also test an unrecognized property.
-  invalidProperties.push("unrecognized_property");
-
-  return invalidProperties;
-}
-
-function checkProperties(actual, expected) {
-  Assert.equal(actual.length, expected.length, `Should have found ${expected.length} invalid properties`);
-  for (let i = 0; i < expected.length; i++) {
-    Assert.ok(actual.includes(expected[i]), `The invalid properties should contain "${expected[i]}"`);
-  }
-}
-
-add_task(function* test_theme_supported_properties() {
-  let additionalInvalidProperties = yield getAdditionalInvalidManifestProperties();
-  let actual = validateThemeManifest([...baseManifestProperties, ...additionalInvalidProperties]);
-  let expected = ["background", "permissions", "content_scripts", ...additionalInvalidProperties];
-  checkProperties(actual, expected);
-});
-
diff --git a/toolkit/components/extensions/test/xpcshell/xpcshell.ini b/toolkit/components/extensions/test/xpcshell/xpcshell.ini
index 4e70b1ef616c..b9cabc3a9922 100644
--- a/toolkit/components/extensions/test/xpcshell/xpcshell.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell.ini
@@ -77,7 +77,6 @@ head = head.js head_sync.js
 skip-if = os == "android"
 [test_ext_storage_sync_crypto.js]
 skip-if = os == "android"
-[test_ext_themes_supported_properties.js]
 [test_ext_topSites.js]
 skip-if = os == "android"
 [test_getAPILevelForWindow.js]