--- a/toolkit/components/extensions/test/mochitest/test_ext_cookies.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_cookies.html
@@ -74,16 +74,19 @@ add_task(async function test_cookies() {
       path: "/",
       secure: false,
       httpOnly: false,
       session: false,
       expirationDate: THE_FUTURE,
       storeId: STORE_ID,
     };
 
+    // Remove all cookies before starting the test.
+    await browser.browsingData.removeCookies({});
+
     let cookie = await browser.cookies.set({url: TEST_URL, name: "name1", value: "value1", expirationDate: THE_FUTURE});
     assertExpected(expected, cookie);
 
     cookie = await browser.cookies.get({url: TEST_URL, name: "name1"});
     assertExpected(expected, cookie);
 
     let cookies = await browser.cookies.getAll({name: "name1"});
     browser.test.assertEq(cookies.length, 1, "one cookie found for matching name");
@@ -254,17 +257,17 @@ add_task(async function test_cookies() {
     }
 
     browser.test.notifyPass("cookies");
   }
 
   let extension = ExtensionTestUtils.loadExtension({
     background,
     manifest: {
-      permissions: ["cookies", "*://example.org/", "webNavigation"],
+      permissions: ["cookies", "*://example.org/", "webNavigation", "browsingData"],
     },
   });
 
   await extension.startup();
   await extension.awaitFinish("cookies");
   await extension.unload();
 });