diff --git a/browser/components/extensions/test/xpcshell/test_ext_manifest.js b/browser/components/extensions/test/xpcshell/test_ext_manifest.js
deleted file mode 100644
index a2a3c79bdadf..000000000000
--- a/browser/components/extensions/test/xpcshell/test_ext_manifest.js
+++ /dev/null
@@ -1,48 +0,0 @@
-/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
-/* vim: set sts=2 sw=2 et tw=80: */
-"use strict";
-
-async function testIconPaths(icon, manifest, expectedError) {
-  let normalized = await ExtensionTestUtils.normalizeManifest(manifest);
-
-  if (expectedError) {
-    ok(expectedError.test(normalized.error),
-       `Should have an error for ${JSON.stringify(manifest)}`);
-  } else {
-    ok(!normalized.error, `Should not have an error ${JSON.stringify(manifest)}, ${normalized.error}`);
-  }
-}
-
-add_task(async function test_manifest() {
-  let badpaths = ["", " ", "\t", "http://foo.com/icon.png"];
-  for (let path of badpaths) {
-    for (let action of ["browser_action", "page_action", "sidebar_action"]) {
-      let manifest = {};
-      manifest[action] = {default_icon: path};
-      let error = new RegExp(`Error processing ${action}.default_icon`);
-      await testIconPaths(path, manifest, error);
-
-      manifest[action] = {default_icon: {"16": path}};
-      await testIconPaths(path, manifest, error);
-    }
-  }
-
-  let paths = ["icon.png", "/icon.png", "./icon.png", "path to an icon.png", " icon.png"];
-  for (let path of paths) {
-    for (let action of ["browser_action", "page_action", "sidebar_action"]) {
-      let manifest = {};
-      manifest[action] = {default_icon: path};
-      if (action == "sidebar_action") {
-        // Sidebar requires panel.
-        manifest[action].default_panel = "foo.html";
-      }
-      await testIconPaths(path, manifest);
-
-      manifest[action] = {default_icon: {"16": path}};
-      if (action == "sidebar_action") {
-        manifest[action].default_panel = "foo.html";
-      }
-      await testIconPaths(path, manifest);
-    }
-  }
-});
diff --git a/browser/components/extensions/test/xpcshell/xpcshell.ini b/browser/components/extensions/test/xpcshell/xpcshell.ini
index 230f60d22590..190b90749e4a 100644
--- a/browser/components/extensions/test/xpcshell/xpcshell.ini
+++ b/browser/components/extensions/test/xpcshell/xpcshell.ini
@@ -17,7 +17,6 @@ dupe-manifest =
 #    For tests which should only run with both remote extensions and remote content.
 
 [test_ext_geckoProfiler_schema.js]
-[test_ext_manifest.js]
 [test_ext_manifest_commands.js]
 [test_ext_manifest_omnibox.js]
 [test_ext_manifest_permissions.js]
diff --git a/toolkit/components/extensions/schemas/manifest.json b/toolkit/components/extensions/schemas/manifest.json
index db1f6a2552e9..2b778a8c5ca3 100644
--- a/toolkit/components/extensions/schemas/manifest.json
+++ b/toolkit/components/extensions/schemas/manifest.json
@@ -95,7 +95,7 @@
             "type": "object",
             "optional": true,
             "patternProperties": {
-              "^[1-9]\\d*$": { "$ref": "ExtensionFileUrl" }
+              "^[1-9]\\d*$": { "type": "string" }
             }
           },
 
diff --git a/toolkit/components/extensions/test/xpcshell/test_ext_manifest.js b/toolkit/components/extensions/test/xpcshell/test_ext_manifest.js
index bde6bff3357d..b21dbda6d585 100644
--- a/toolkit/components/extensions/test/xpcshell/test_ext_manifest.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_manifest.js
@@ -2,42 +2,48 @@
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
-async function testIconPaths(icon, manifest, expectedError) {
-  let normalized = await ExtensionTestUtils.normalizeManifest(manifest);
-
-  if (expectedError) {
-    ok(expectedError.test(normalized.error),
-       `Should have an error for ${JSON.stringify(icon)}`);
-  } else {
-    ok(!normalized.error, `Should not have an error ${JSON.stringify(icon)}`);
-  }
-}
-
 add_task(async function test_manifest() {
   let badpaths = ["", " ", "\t", "http://foo.com/icon.png"];
   for (let path of badpaths) {
-    await testIconPaths(path, {
-      "icons": path,
-    }, /Error processing icons/);
-
-    await testIconPaths(path, {
-      "icons": {
-        "16": path,
+    let normalized = await ExtensionTestUtils.normalizeManifest({
+      "browser_action": {
+        "default_icon": path,
       },
-    }, /Error processing icons/);
+    });
+
+    ok(/Error processing browser_action.default_icon/.test(normalized.error),
+       `Should have an error for ${JSON.stringify(path)}`);
+
+    normalized = await ExtensionTestUtils.normalizeManifest({
+      "browser_action": {
+        "default_icon": {
+          "16": path,
+        },
+      },
+    });
+
+    ok(/Error processing browser_action.default_icon/.test(normalized.error),
+       `Should have an error for ${JSON.stringify(path)}`);
   }
 
   let paths = ["icon.png", "/icon.png", "./icon.png", "path to an icon.png", " icon.png"];
   for (let path of paths) {
-    // manifest.icons is an object
-    await testIconPaths(path, {
-      "icons": path,
-    }, /Error processing icons/);
-
-    await testIconPaths(path, {
-      "icons": {
-        "16": path,
+    let normalized = await ExtensionTestUtils.normalizeManifest({
+      "browser_action": {
+        "default_icon": {
+          "16": path,
+        },
       },
     });
+
+    ok(!normalized.error, `Should not have an error ${JSON.stringify(path)}`);
+
+    normalized = await ExtensionTestUtils.normalizeManifest({
+      "browser_action": {
+        "default_icon": path,
+      },
+    });
+
+    ok(!normalized.error, `Should not have an error ${JSON.stringify(path)}`);
   }
 });