diff --git a/netwerk/base/PrivateBrowsingChannel.h b/netwerk/base/PrivateBrowsingChannel.h
index 165bea03c46..0fe96bd1a29 100644
--- a/netwerk/base/PrivateBrowsingChannel.h
+++ b/netwerk/base/PrivateBrowsingChannel.h
@@ -48,7 +48,7 @@ public:
   NS_IMETHOD GetIsChannelPrivate(bool *aResult)
   {
       NS_ENSURE_ARG_POINTER(aResult);
-      *aResult = NS_UsePrivateBrowsing(static_cast<Channel*>(this));
+      *aResult = mPrivateBrowsing;
       return NS_OK;
   }
 
@@ -63,6 +63,21 @@ public:
       return NS_OK;
   }
 
+  // Must be called every time the channel's callbacks or loadGroup is updated
+  void UpdatePrivateBrowsing()
+  {
+      // once marked as private we never go un-private
+      if (mPrivateBrowsing) {
+          return;
+      }
+
+      nsCOMPtr<nsILoadContext> loadContext;
+      NS_QueryNotificationCallbacks(static_cast<Channel*>(this), loadContext);
+      if (loadContext) {
+          mPrivateBrowsing = loadContext->UsePrivateBrowsing();
+      }
+  }
+
   bool CanSetCallbacks(nsIInterfaceRequestor* aCallbacks) const
   {
       // Make sure that the private bit override flag is not set.
diff --git a/netwerk/base/nsBaseChannel.cpp b/netwerk/base/nsBaseChannel.cpp
index 4bf5dc076ae..0a6829349b2 100644
--- a/netwerk/base/nsBaseChannel.cpp
+++ b/netwerk/base/nsBaseChannel.cpp
@@ -101,7 +101,7 @@ nsBaseChannel::Redirect(nsIChannel *newChannel, uint32_t redirectFlags,
     newChannel->SetLoadInfo(nullptr);
   }
 
-  // Try to preserve the privacy bit if it has been overridden
+  // Preserve the privacy bit if it has been overridden
   if (mPrivateBrowsingOverriden) {
     nsCOMPtr<nsIPrivateBrowsingChannel> newPBChannel =
       do_QueryInterface(newChannel);
@@ -424,6 +424,7 @@ nsBaseChannel::SetLoadGroup(nsILoadGroup *aLoadGroup)
 
   mLoadGroup = aLoadGroup;
   CallbacksChanged();
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
@@ -497,6 +498,7 @@ nsBaseChannel::SetNotificationCallbacks(nsIInterfaceRequestor *aCallbacks)
 
   mCallbacks = aCallbacks;
   CallbacksChanged();
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
diff --git a/netwerk/base/nsNetUtil.cpp b/netwerk/base/nsNetUtil.cpp
index a1a7025b802..6991af98f89 100644
--- a/netwerk/base/nsNetUtil.cpp
+++ b/netwerk/base/nsNetUtil.cpp
@@ -1220,13 +1220,12 @@ bool
 NS_UsePrivateBrowsing(nsIChannel *channel)
 {
     bool isPrivate = false;
-    bool isOverriden = false;
     nsCOMPtr<nsIPrivateBrowsingChannel> pbChannel = do_QueryInterface(channel);
-    if (pbChannel &&
-        NS_SUCCEEDED(pbChannel->IsPrivateModeOverriden(&isPrivate, &isOverriden)) &&
-        isOverriden) {
+    if (pbChannel && NS_SUCCEEDED(pbChannel->GetIsChannelPrivate(&isPrivate))) {
         return isPrivate;
     }
+
+    // Some channels may not implement nsIPrivateBrowsingChannel
     nsCOMPtr<nsILoadContext> loadContext;
     NS_QueryNotificationCallbacks(channel, loadContext);
     return loadContext && loadContext->UsePrivateBrowsing();
diff --git a/netwerk/protocol/http/HttpBaseChannel.cpp b/netwerk/protocol/http/HttpBaseChannel.cpp
index 3cbda7ed274..046a45059fd 100644
--- a/netwerk/protocol/http/HttpBaseChannel.cpp
+++ b/netwerk/protocol/http/HttpBaseChannel.cpp
@@ -261,7 +261,7 @@ HttpBaseChannel::SetLoadGroup(nsILoadGroup *aLoadGroup)
 
   mLoadGroup = aLoadGroup;
   mProgressSink = nullptr;
-  mPrivateBrowsing = NS_UsePrivateBrowsing(this);
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
@@ -419,7 +419,7 @@ HttpBaseChannel::SetNotificationCallbacks(nsIInterfaceRequestor *aCallbacks)
   mCallbacks = aCallbacks;
   mProgressSink = nullptr;
 
-  mPrivateBrowsing = NS_UsePrivateBrowsing(this);
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
diff --git a/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp b/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
index c7a55275b42..f4f7c1a266e 100644
--- a/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
+++ b/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
@@ -433,6 +433,8 @@ WyciwygChannelChild::SetLoadGroup(nsILoadGroup * aLoadGroup)
                                 mLoadGroup,
                                 NS_GET_IID(nsIProgressEventSink),
                                 getter_AddRefs(mProgressSink));
+
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
@@ -525,6 +527,7 @@ WyciwygChannelChild::SetNotificationCallbacks(nsIInterfaceRequestor * aCallbacks
                                 mLoadGroup,
                                 NS_GET_IID(nsIProgressEventSink),
                                 getter_AddRefs(mProgressSink));
+  UpdatePrivateBrowsing();
   return NS_OK;
 }
 
diff --git a/netwerk/protocol/wyciwyg/nsWyciwygChannel.cpp b/netwerk/protocol/wyciwyg/nsWyciwygChannel.cpp
index 20e69e660d8..dd58105547c 100644
--- a/netwerk/protocol/wyciwyg/nsWyciwygChannel.cpp
+++ b/netwerk/protocol/wyciwyg/nsWyciwygChannel.cpp
@@ -231,7 +231,7 @@ nsWyciwygChannel::SetLoadGroup(nsILoadGroup* aLoadGroup)
                                 mLoadGroup,
                                 NS_GET_IID(nsIProgressEventSink),
                                 getter_AddRefs(mProgressSink));
-  mPrivateBrowsing = NS_UsePrivateBrowsing(this);
+  UpdatePrivateBrowsing();
   NS_GetOriginAttributes(this, mOriginAttributes);
 
   return NS_OK;
@@ -328,7 +328,7 @@ nsWyciwygChannel::SetNotificationCallbacks(nsIInterfaceRequestor* aNotificationC
                                 NS_GET_IID(nsIProgressEventSink),
                                 getter_AddRefs(mProgressSink));
 
-  mPrivateBrowsing = NS_UsePrivateBrowsing(this);
+  UpdatePrivateBrowsing();
   NS_GetOriginAttributes(this, mOriginAttributes);
 
   return NS_OK;