diff -up firefox-53.0/dom/media/webrtc/MediaEngine.h.1335250 firefox-53.0/dom/media/webrtc/MediaEngine.h
--- firefox-53.0/dom/media/webrtc/MediaEngine.h.1335250	2017-04-11 06:15:22.000000000 +0200
+++ firefox-53.0/dom/media/webrtc/MediaEngine.h	2017-04-19 20:35:55.264741939 +0200
@@ -226,7 +226,7 @@ public:
     ~AllocationHandle() {}
   public:
     AllocationHandle(const dom::MediaTrackConstraints& aConstraints,
-                     const ipc::PrincipalInfo& aPrincipalInfo,
+                     const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
                      const MediaEnginePrefs& aPrefs,
                      const nsString& aDeviceId)
 
@@ -236,7 +236,7 @@ public:
       mDeviceId(aDeviceId) {}
   public:
     NormalizedConstraints mConstraints;
-    ipc::PrincipalInfo mPrincipalInfo;
+    mozilla::ipc::PrincipalInfo mPrincipalInfo;
     MediaEnginePrefs mPrefs;
     nsString mDeviceId;
   };
@@ -327,7 +327,7 @@ public:
   virtual nsresult Allocate(const dom::MediaTrackConstraints &aConstraints,
                             const MediaEnginePrefs &aPrefs,
                             const nsString& aDeviceId,
-                            const ipc::PrincipalInfo& aPrincipalInfo,
+                            const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
                             AllocationHandle** aOutHandle,
                             const char** aOutBadConstraint)
   {