--- a/netwerk/base/nsNetUtil.cpp
+++ b/netwerk/base/nsNetUtil.cpp
@@ -2403,16 +2403,28 @@ NS_CompareLoadInfoAndLoadContext(nsIChan
                     spec.EqualsLiteral("about:sync-tabs");
     }
   }
 
   if (isAboutPage) {
     return NS_OK;
   }
 
+  // We skip the favicon loading here. The favicon loading might be
+  // triggered by the XUL image. For that case, the loadContext will have
+  // default originAttributes since the XUL image uses SystemPrincipal, but
+  // the loadInfo will use originAttributes from the content. Thus, the
+  // originAttributes between loadInfo and loadContext will be different.
+  // That's why we have to skip the comparison for the favicon loading.
+  if (nsContentUtils::IsSystemPrincipal(loadInfo->LoadingPrincipal()) &&
+      loadInfo->InternalContentPolicyType() ==
+        nsIContentPolicy::TYPE_INTERNAL_IMAGE_FAVICON) {
+    return NS_OK;
+  }
+
   uint32_t loadContextAppId = 0;
   nsresult rv = loadContext->GetAppId(&loadContextAppId);
   if (NS_FAILED(rv)) {
     return NS_ERROR_UNEXPECTED;
   }
 
   bool loadContextIsInBE = false;
   rv = loadContext->GetIsInIsolatedMozBrowserElement(&loadContextIsInBE);

--- a/netwerk/protocol/http/HttpBaseChannel.cpp
+++ b/netwerk/protocol/http/HttpBaseChannel.cpp
@@ -2659,28 +2659,43 @@ HttpBaseChannel::ShouldIntercept(nsIURI*
                                                         &shouldIntercept);
     if (NS_FAILED(rv)) {
       return false;
     }
   }
   return shouldIntercept;
 }
 
-void HttpBaseChannel::CheckPrivateBrowsing()
+#ifdef DEBUG
+void HttpBaseChannel::AssertPrivateBrowsingId()
 {
   nsCOMPtr<nsILoadContext> loadContext;
   NS_QueryNotificationCallbacks(this, loadContext);
   // For addons it's possible that mLoadInfo is null.
-  if (mLoadInfo && loadContext) {
-      DocShellOriginAttributes docShellAttrs;
-      loadContext->GetOriginAttributes(docShellAttrs);
-      MOZ_ASSERT(mLoadInfo->GetOriginAttributes().mPrivateBrowsingId == docShellAttrs.mPrivateBrowsingId,
-                 "PrivateBrowsingId values are not the same between LoadInfo and LoadContext.");
+  if (!mLoadInfo) {
+    return;
+  }
+
+  if (!loadContext) {
+    return;
   }
+
+  // We skip testing of favicon loading here since it could be triggered by XUL image
+  // which uses SystemPrincipal. The SystemPrincpal doesn't have mPrivateBrowsingId.
+  if (nsContentUtils::IsSystemPrincipal(mLoadInfo->LoadingPrincipal()) &&
+      mLoadInfo->InternalContentPolicyType() == nsIContentPolicy::TYPE_INTERNAL_IMAGE_FAVICON) {
+    return;
+  }
+
+  DocShellOriginAttributes docShellAttrs;
+  loadContext->GetOriginAttributes(docShellAttrs);
+  MOZ_ASSERT(mLoadInfo->GetOriginAttributes().mPrivateBrowsingId == docShellAttrs.mPrivateBrowsingId,
+             "PrivateBrowsingId values are not the same between LoadInfo and LoadContext.");
 }
+#endif
 
 //-----------------------------------------------------------------------------
 // nsHttpChannel::nsITraceableChannel
 //-----------------------------------------------------------------------------
 
 NS_IMETHODIMP
 HttpBaseChannel::SetNewListener(nsIStreamListener *aListener, nsIStreamListener **_retval)
 {

--- a/netwerk/protocol/http/HttpBaseChannel.h
+++ b/netwerk/protocol/http/HttpBaseChannel.h
@@ -377,18 +377,20 @@ protected:
   nsIPrincipal *GetURIPrincipal();
 
   bool BypassServiceWorker() const;
 
   // Returns true if this channel should intercept the network request and prepare
   // for a possible synthesized response instead.
   bool ShouldIntercept(nsIURI* aURI = nullptr);
 
+#ifdef DEBUG
   // Check if mPrivateBrowsingId matches between LoadInfo and LoadContext.
-  void CheckPrivateBrowsing();
+  void AssertPrivateBrowsingId();
+#endif
 
   friend class PrivateBrowsingChannel<HttpBaseChannel>;
   friend class InterceptFailedOnStop;
 
   nsCOMPtr<nsIURI>                  mURI;
   nsCOMPtr<nsIURI>                  mOriginalURI;
   nsCOMPtr<nsIURI>                  mDocumentURI;
   nsCOMPtr<nsIStreamListener>       mListener;

--- a/netwerk/protocol/http/HttpChannelChild.cpp
+++ b/netwerk/protocol/http/HttpChannelChild.cpp
@@ -1791,17 +1791,17 @@ HttpChannelChild::AsyncOpen(nsIStreamLis
              mLoadInfo->GetInitialSecurityCheckDone() ||
              (mLoadInfo->GetSecurityMode() == nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL &&
               nsContentUtils::IsSystemPrincipal(mLoadInfo->LoadingPrincipal())),
              "security flags in loadInfo but asyncOpen2() not called");
 
   LOG(("HttpChannelChild::AsyncOpen [this=%p uri=%s]\n", this, mSpec.get()));
 
 #ifdef DEBUG
-  CheckPrivateBrowsing();
+  AssertPrivateBrowsingId();
 #endif
 
   if (mCanceled)
     return mStatus;
 
   NS_ENSURE_TRUE(gNeckoChild != nullptr, NS_ERROR_FAILURE);
   NS_ENSURE_ARG_POINTER(listener);
   NS_ENSURE_TRUE(!mIsPending, NS_ERROR_IN_PROGRESS);

--- a/netwerk/protocol/http/nsHttpChannel.cpp
+++ b/netwerk/protocol/http/nsHttpChannel.cpp
@@ -5654,17 +5654,17 @@ nsHttpChannel::AsyncOpen(nsIStreamListen
                 nsContentUtils::IsSystemPrincipal(mLoadInfo->LoadingPrincipal())),
                "security flags in loadInfo but asyncOpen2() not called");
 
     LOG(("nsHttpChannel::AsyncOpen [this=%p]\n", this));
 
     NS_CompareLoadInfoAndLoadContext(this);
 
 #ifdef DEBUG
-    CheckPrivateBrowsing();
+    AssertPrivateBrowsingId();
 #endif
 
     NS_ENSURE_ARG_POINTER(listener);
     NS_ENSURE_TRUE(!mIsPending, NS_ERROR_IN_PROGRESS);
     NS_ENSURE_TRUE(!mWasOpened, NS_ERROR_ALREADY_OPENED);
 
     nsresult rv;