--- a/layout/style/FontFaceSet.cpp
+++ b/layout/style/FontFaceSet.cpp
@@ -612,30 +612,35 @@ FontFaceSet::StartLoad(gfxUserFontEntry*
          fontLoader.get(), aFontFaceSrc->mURI->GetSpecOrDefault().get(),
          aFontFaceSrc->mReferrer
          ? aFontFaceSrc->mReferrer->GetSpecOrDefault().get()
          : ""));
   }
 
   nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
   if (httpChannel) {
-    httpChannel->SetReferrerWithPolicy(aFontFaceSrc->mReferrer,
-                                       mDocument->GetReferrerPolicy());
+    rv = httpChannel->SetReferrerWithPolicy(aFontFaceSrc->mReferrer,
+                                            mDocument->GetReferrerPolicy());
+    NS_ENSURE_SUCCESS(rv, rv);
+
     nsAutoCString accept("application/font-woff;q=0.9,*/*;q=0.8");
     if (Preferences::GetBool(GFX_PREF_WOFF2_ENABLED)) {
       accept.Insert(NS_LITERAL_CSTRING("application/font-woff2;q=1.0,"), 0);
     }
-    httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
-                                  accept, false);
+    rv = httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
+                                       accept, false);
+    NS_ENSURE_SUCCESS(rv, rv);
+
     // For WOFF and WOFF2, we should tell servers/proxies/etc NOT to try
     // and apply additional compression at the content-encoding layer
     if (aFontFaceSrc->mFormatFlags & (gfxUserFontSet::FLAG_FORMAT_WOFF |
                                       gfxUserFontSet::FLAG_FORMAT_WOFF2)) {
-      httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept-Encoding"),
-                                    NS_LITERAL_CSTRING("identity"), false);
+      rv = httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept-Encoding"),
+                                         NS_LITERAL_CSTRING("identity"), false);
+      NS_ENSURE_SUCCESS(rv, rv);
     }
   }
   nsCOMPtr<nsISupportsPriority> priorityChannel(do_QueryInterface(channel));
   if (priorityChannel) {
     priorityChannel->AdjustPriority(nsISupportsPriority::PRIORITY_HIGH);
   }
 
   rv = NS_NewStreamLoader(getter_AddRefs(streamLoader), fontLoader);

--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -1680,27 +1680,32 @@ Loader::LoadSheet(SheetLoadData* aLoadDa
     if (cos) {
       cos->AddClassFlags(nsIClassOfService::Leader);
     }
   }
 
   nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
   if (httpChannel) {
     // Send a minimal Accept header for text/css
-    httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
-                                  NS_LITERAL_CSTRING("text/css,*/*;q=0.1"),
-                                  false);
+    rv = httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
+                                       NS_LITERAL_CSTRING("text/css,*/*;q=0.1"),
+                                       false);
+    NS_ENSURE_SUCCESS(rv, rv);
+
     nsCOMPtr<nsIURI> referrerURI = aLoadData->GetReferrerURI();
-    if (referrerURI)
-      httpChannel->SetReferrerWithPolicy(referrerURI,
-                                         aLoadData->mSheet->GetReferrerPolicy());
+    if (referrerURI) {
+      rv = httpChannel->SetReferrerWithPolicy(referrerURI,
+                                              aLoadData->mSheet->GetReferrerPolicy());
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
 
     nsCOMPtr<nsIHttpChannelInternal> internalChannel = do_QueryInterface(httpChannel);
     if (internalChannel) {
-      internalChannel->SetIntegrityMetadata(sriMetadata.GetIntegrityString());
+      rv = internalChannel->SetIntegrityMetadata(sriMetadata.GetIntegrityString());
+      NS_ENSURE_SUCCESS(rv, rv);
     }
 
     // Set the initiator type
     nsCOMPtr<nsITimedChannel> timedChannel(do_QueryInterface(httpChannel));
     if (timedChannel) {
       if (aLoadData->mParentData) {
         timedChannel->SetInitiatorType(NS_LITERAL_STRING("css"));
       } else {