--- a/dom/base/PerformanceObserver.cpp
+++ b/dom/base/PerformanceObserver.cpp
@@ -130,20 +130,19 @@ PerformanceObserver::QueueEntry(Performa
   aEntry->GetEntryType(entryType);
   if (!mEntryTypes.Contains<nsString>(entryType)) {
     return;
   }
 
   mQueuedEntries.AppendElement(aEntry);
 }
 
-static const char16_t* sValidTypeNames[5] = {
+static const char16_t* sValidTypeNames[4] = {
   MOZ_UTF16("mark"),
   MOZ_UTF16("measure"),
-  MOZ_UTF16("navigation"),
   MOZ_UTF16("resource"),
   MOZ_UTF16("server")
 };
 
 void
 PerformanceObserver::Observe(const PerformanceObserverInit& aOptions,
                              ErrorResult& aRv)
 {

--- a/dom/tests/mochitest/general/test_interfaces.html
+++ b/dom/tests/mochitest/general/test_interfaces.html
@@ -903,16 +903,20 @@ var interfaceNamesInGlobalScope =
     "PerformanceEntry",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMark",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMeasure",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceNavigation",
 // IMPORTANT: Do not change this list without review from a DOM peer!
+    {name: "PerformanceObserver", nightly: true},
+// IMPORTANT: Do not change this list without review from a DOM peer!
+    {name: "PerformanceObserverEntryList", nightly: true},
+// IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceResourceTiming",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceTiming",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PeriodicWave",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "Permissions",
 // IMPORTANT: Do not change this list without review from a DOM peer!

--- a/dom/webidl/PerformanceObserver.webidl
+++ b/dom/webidl/PerformanceObserver.webidl
@@ -1,15 +1,15 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/.
  *
  * The origin of this IDL file is
- * https://w3c.github.io/performance-timeline/#the-performance-observer-interface
+ * https://w3c.github.io/performance-timeline/#the-performanceobserver-interface
  */
 
 dictionary PerformanceObserverInit {
   required sequence<DOMString> entryTypes;
 };
 
 callback PerformanceObserverCallback = void (PerformanceObserverEntryList entries, PerformanceObserver observer);
 

--- a/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js
+++ b/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js
@@ -168,16 +168,20 @@ var interfaceNamesInGlobalScope =
     "Performance",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceEntry",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMark",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMeasure",
 // IMPORTANT: Do not change this list without review from a DOM peer!
+    { name: "PerformanceObserver", nightly: true },
+// IMPORTANT: Do not change this list without review from a DOM peer!
+    { name: "PerformanceObserverEntryList", nightly: true },
+// IMPORTANT: Do not change this list without review from a DOM peer!
     "Promise",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushEvent", b2g: false, android: false, nightlyAndroid: true },
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushManager", b2g: false, android: false, nightlyAndroid: true },
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushMessageData", b2g: false, android: false, nightlyAndroid: true },
 // IMPORTANT: Do not change this list without review from a DOM peer!

--- a/dom/workers/test/test_worker_interfaces.js
+++ b/dom/workers/test/test_worker_interfaces.js
@@ -158,16 +158,20 @@ var interfaceNamesInGlobalScope =
     "Performance",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceEntry",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMark",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "PerformanceMeasure",
 // IMPORTANT: Do not change this list without review from a DOM peer!
+    { name: "PerformanceObserver", nightly: true },
+// IMPORTANT: Do not change this list without review from a DOM peer!
+    { name: "PerformanceObserverEntryList", nightly: true },
+// IMPORTANT: Do not change this list without review from a DOM peer!
     "Promise",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushManager", b2g: false, nightlyAndroid: true, android: false },
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushSubscription", b2g: false, nightlyAndroid: true, android: false },
 // IMPORTANT: Do not change this list without review from a DOM peer!
     { name: "PushSubscriptionOptions", b2g: false, nightlyAndroid: true, android: false },
 // IMPORTANT: Do not change this list without review from a DOM peer!

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -162,16 +162,23 @@ pref("dom.enable_resource_timing", true)
 pref("dom.enable_user_timing", true);
 
 // Enable printing performance marks/measures to log
 pref("dom.performance.enable_user_timing_logging", false);
 
 // Enable notification of performance timing
 pref("dom.performance.enable_notify_performance_timing", false);
 
+// Enable Performance Observer API
+#ifdef NIGHTLY_BUILD
+pref("dom.enable_performance_observer", true);
+#else
+pref("dom.enable_performance_observer", false);
+#endif
+
 // Whether the Gamepad API is enabled
 pref("dom.gamepad.enabled", true);
 #ifdef RELEASE_BUILD
 pref("dom.gamepad.non_standard_events.enabled", false);
 #else
 pref("dom.gamepad.non_standard_events.enabled", true);
 #endif
 

deleted file mode 100644
--- a/testing/web-platform/meta/performance-timeline/idlharness.html.ini
+++ /dev/null
@@ -1,47 +0,0 @@
-[idlharness.html]
-  type: testharness
-  [PerformanceObserverEntryList interface: existence and properties of interface object]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface object length]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface object name]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface: existence and properties of interface prototype object]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface: existence and properties of interface prototype object's "constructor" property]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface: operation getEntries(PerformanceEntryFilterOptions)]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface: operation getEntriesByType(DOMString)]
-    expected: FAIL
-
-  [PerformanceObserverEntryList interface: operation getEntriesByName(DOMString,DOMString)]
-    expected: FAIL
-
-  [PerformanceObserver interface: existence and properties of interface object]
-    expected: FAIL
-
-  [PerformanceObserver interface object length]
-    expected: FAIL
-
-  [PerformanceObserver interface object name]
-    expected: FAIL
-
-  [PerformanceObserver interface: existence and properties of interface prototype object]
-    expected: FAIL
-
-  [PerformanceObserver interface: existence and properties of interface prototype object's "constructor" property]
-    expected: FAIL
-
-  [PerformanceObserver interface: operation observe(PerformanceObserverInit)]
-    expected: FAIL
-
-  [PerformanceObserver interface: operation disconnect()]
-    expected: FAIL
-

--- a/testing/web-platform/meta/performance-timeline/po-disconnect.html.ini
+++ b/testing/web-platform/meta/performance-timeline/po-disconnect.html.ini
@@ -1,11 +1,6 @@
 [po-disconnect.html]
   type: testharness
-  [disconnected callbacks must not be invoked]
-    expected: FAIL
+  expected: TIMEOUT
+  [An observer disconnected after a mark must receive the mark]
+    expected: TIMEOUT
 
-  [disconnecting an unconnected observer is a no-op]
-    expected: FAIL
-
-  [An observer disconnected after a mark must receive the mark]
-    expected: FAIL
-

deleted file mode 100644
--- a/testing/web-platform/meta/performance-timeline/po-mark-measure.html.ini
+++ /dev/null
@@ -1,11 +0,0 @@
-[po-mark-measure.html]
-  type: testharness
-  [entries are observable]
-    expected: FAIL
-
-  [mark entries are observable]
-    expected: FAIL
-
-  [measure entries are observable]
-    expected: FAIL
-

deleted file mode 100644
--- a/testing/web-platform/meta/performance-timeline/po-observe.html.ini
+++ /dev/null
@@ -1,14 +0,0 @@
-[po-observe.html]
-  type: testharness
-  [no entryTypes throws a TypeError]
-    expected: FAIL
-
-  [Empty sequence entryTypes throws a TypeError]
-    expected: FAIL
-
-  [Filter unsupported entryType entryType names within the entryTypes sequence]
-    expected: FAIL
-
-  [replace observer if already present]
-    expected: FAIL
-

deleted file mode 100644
--- a/testing/web-platform/meta/performance-timeline/po-resource.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[po-resource.html]
-  type: testharness
-  [resource entries are observable]
-    expected: FAIL
-