--- a/netwerk/test/browser/browser.ini
+++ b/netwerk/test/browser/browser.ini
@@ -5,8 +5,9 @@ support-files =
 [browser_about_cache.js]
 [browser_NetUtil.js]
 [browser_child_resource.js]
 skip-if = !crashreporter || (e10s && debug && os == "linux" && bits == 64) || debug # Bug 1370783
 [browser_post_file.js]
 [browser_nsIFormPOSTActionChannel.js]
 skip-if = e10s # protocol handler and channel does not work in content process
 [browser_resource_navigation.js]
+[browser_cookie_sync_across_tabs.js]

new file mode 100644
--- /dev/null
+++ b/netwerk/test/browser/browser_cookie_sync_across_tabs.js
@@ -0,0 +1,65 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+"use strict";
+
+add_task(async function() {
+  info("Make sure cookie changes in one process are visible in the other");
+
+  const kRoot = getRootDirectory(gTestPath).replace("chrome://mochitests/content/",
+                                                    "https://example.com/");
+  const kTestPage = kRoot + "dummy.html";
+
+  Services.cookies.removeAll();
+
+  let tab1 = await BrowserTestUtils.openNewForegroundTab({ gBrowser, url: kTestPage, forceNewProcess: true });
+  let tab2 = await BrowserTestUtils.openNewForegroundTab({ gBrowser, url: kTestPage, forceNewProcess: true });
+
+  let browser1 = gBrowser.getBrowserForTab(tab1);
+  let browser2 = gBrowser.getBrowserForTab(tab2);
+
+  let pid1 = browser1.frameLoader.tabParent.osPid;
+  let pid2 = browser2.frameLoader.tabParent.osPid;
+
+  // Note, this might not be true once fission is implemented (Bug 1451850)
+  ok(pid1 != pid2, "We should have different processes here.");
+
+  await ContentTask.spawn(browser1, null, async function() {
+    is(content.document.cookie, "", "Expecting no cookies");
+  });
+
+  await ContentTask.spawn(browser2, null, async function() {
+    is(content.document.cookie, "", "Expecting no cookies");
+  });
+
+  await ContentTask.spawn(browser1, null, async function() {
+    content.document.cookie = "a1=test";
+  });
+
+  await ContentTask.spawn(browser2, null, async function() {
+    is(content.document.cookie, "a1=test", "Cookie should be set");
+    content.document.cookie = "a1=other_test";
+  });
+
+  await ContentTask.spawn(browser1, null, async function() {
+    is(content.document.cookie, "a1=other_test", "Cookie should be set");
+    content.document.cookie = "a2=again";
+  });
+
+  await ContentTask.spawn(browser2, null, async function() {
+    is(content.document.cookie, "a1=other_test; a2=again", "Cookie should be set");
+    content.document.cookie = "a1=; expires=Thu, 01-Jan-1970 00:00:01 GMT;";
+    content.document.cookie = "a2=; expires=Thu, 01-Jan-1970 00:00:01 GMT;";
+  });
+
+  await ContentTask.spawn(browser1, null, async function() {
+    is(content.document.cookie, "", "Cookies should be cleared");
+  });
+
+  BrowserTestUtils.removeTab(tab1);
+  BrowserTestUtils.removeTab(tab2);
+
+  ok(true, "Got to the end of the test!");
+});