--- a/browser/base/content/test/plugins/browser.ini
+++ b/browser/base/content/test/plugins/browser.ini
@@ -3,16 +3,17 @@ support-files =
   blocklist_proxy.js
   blockNoPlugins.xml
   blockPluginHard.xml
   blockPluginInfoURL.xml
   blockPluginVulnerableNoUpdate.xml
   blockPluginVulnerableUpdatable.xml
   browser_clearplugindata.html
   browser_clearplugindata_noage.html
+  empty_file.html
   head.js
   plugin_add_dynamically.html
   plugin_alternate_content.html
   plugin_big.html
   plugin_both.html
   plugin_both2.html
   plugin_bug744745.html
   plugin_bug749455.html
@@ -87,16 +88,17 @@ tags = blocklist
 tags = blocklist
 [browser_pluginnotification.js]
 tags = blocklist
 [browser_plugin_reloading.js]
 tags = blocklist
 [browser_blocklist_content.js]
 skip-if = !e10s
 tags = blocklist
+[browser_enable_DRM_prompt.js]
 [browser_globalplugin_crashinfobar.js]
 skip-if = !crashreporter
 [browser_pluginCrashCommentAndURL.js]
 skip-if = !crashreporter
 [browser_pageInfo_plugins.js]
 [browser_pluginCrashReportNonDeterminism.js]
 skip-if = !crashreporter || os == 'linux' # Bug 1152811
 [browser_private_clicktoplay.js]

new file mode 100644
--- /dev/null
+++ b/browser/base/content/test/plugins/browser_enable_DRM_prompt.js
@@ -0,0 +1,67 @@
+/*
+ * Bug 1366167 - Tests that the "Enable DRM" prompt shows if EME is requested while EME is disabled.
+ */
+
+const TEST_URL =
+  getRootDirectory(gTestPath).replace("chrome://mochitests/content",
+  "https://example.com") + "empty_file.html";
+
+add_task(async function() {
+  await BrowserTestUtils.withNewTab(TEST_URL, async function(browser) {
+    // Note: SpecialPowers.pushPrefEnv has problems with the "Enable DRM"
+    // button on the notification box toggling the prefs. So manually
+    // set/unset the prefs the UI we're testing toggles.
+    let emeWasEnabled = Services.prefs.getBoolPref("media.eme.enabled", false);
+    let cdmWasEnabled = Services.prefs.getBoolPref("media.gmp-widevinecdm.enabled", false);
+
+    // Restore the preferences to their pre-test state on test finish.
+    registerCleanupFunction(function() {
+        Services.prefs.setBoolPref("media.eme.enabled", emeWasEnabled);
+        Services.prefs.setBoolPref("media.gmp-widevinecdm.enabled", cdmWasEnabled);
+    });
+
+    // Turn off EME and Widevine CDM.
+    Services.prefs.setBoolPref("media.eme.enabled", false);
+    Services.prefs.setBoolPref("media.gmp-widevinecdm.enabled", false);
+
+    // Have content request access to Widevine, UI should drop down to
+    // prompt user to enable DRM.
+    let result = await ContentTask.spawn(browser, {}, async function() {
+      try {
+        let config = [{
+          initDataTypes: ["webm"],
+          videoCapabilities: [{contentType: 'video/webm; codecs="vp9"'}],
+        }];
+        await content.navigator.requestMediaKeySystemAccess("com.widevine.alpha", config);
+      } catch (ex) {
+        return {rejected: true};
+      }
+      return {rejected: false};
+    });
+    is(result.rejected, true, "EME request should be denied because EME disabled.");
+
+    // Verify the UI prompt showed.
+    let box = gBrowser.getNotificationBox(browser);
+    let notification = box.currentNotification;
+
+    ok(notification, "Notification should be visible");
+    is(notification.value, "drmContentDisabled",
+       "Should be showing the right notification");
+
+    // Verify the "Enable DRM" button is there.
+    let buttons = notification.querySelectorAll(".notification-button");
+    is(buttons.length, 1, "Should have one button.");
+
+    // Prepare a Promise that should resolve when the "Enable DRM" button's
+    // page reload completes.
+    let refreshPromise = BrowserTestUtils.browserLoaded(browser);
+    buttons[0].click();
+
+    // Wait for the reload to complete.
+    await refreshPromise;
+
+    // Verify clicking the "Enable DRM" button enabled DRM.
+    let enabled = Services.prefs.getBoolPref("media.eme.enabled", true);
+    is(enabled, true, "EME should be enabled after click on 'Enable DRM' button");
+  });
+});

new file mode 100644
--- /dev/null
+++ b/browser/base/content/test/plugins/empty_file.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="UTF-8">
+  </head>
+  <body>
+    This page is intentionally left blank.
+  </body>
+</html>