--- a/toolkit/components/antitracking/AntiTrackingUtils.cpp
+++ b/toolkit/components/antitracking/AntiTrackingUtils.cpp
@@ -559,24 +559,37 @@ void AntiTrackingUtils::ComputeIsThirdPa
   if (policyType == nsIContentPolicy::TYPE_DOCUMENT) {
     loadInfo->SetIsThirdPartyContextToTopWindow(false);
     return;
   }
 
   RefPtr<BrowsingContext> bc;
   loadInfo->GetBrowsingContext(getter_AddRefs(bc));
 
-  // In xpcshell-tests we don't always have a browsingContext.
+  nsCOMPtr<nsIURI> uri;
+  Unused << aChannel->GetURI(getter_AddRefs(uri));
+
+  // In some cases we don't have a browsingContext. For example, in xpcshell
+  // tests or channels that are used to download images.
   if (!bc) {
+    // We turn to check the loading principal if there is no browsing context.
+    auto* loadingPrincipal =
+        BasePrincipal::Cast(loadInfo->GetLoadingPrincipal());
+
+    if (uri && loadingPrincipal) {
+      bool isThirdParty = true;
+      nsresult rv = loadingPrincipal->IsThirdPartyURI(uri, &isThirdParty);
+
+      if (NS_SUCCEEDED(rv)) {
+        loadInfo->SetIsThirdPartyContextToTopWindow(isThirdParty);
+      }
+    }
     return;
   }
 
-  nsCOMPtr<nsIURI> uri;
-  Unused << aChannel->GetURI(getter_AddRefs(uri));
-
   RefPtr<WindowGlobalParent> topWindow =
       GetTopWindowExcludingExtensionAccessibleContentFrames(bc->Canonical(),
                                                             uri);
 
   if (NS_WARN_IF(!topWindow)) {
     return;
   }