--- a/layout/style/nsLayoutStylesheetCache.cpp
+++ b/layout/style/nsLayoutStylesheetCache.cpp
@@ -251,20 +251,20 @@ nsLayoutStylesheetCache::DesignModeSheet
   return mDesignModeSheet;
 }
 
 void
 nsLayoutStylesheetCache::Shutdown()
 {
   gCSSLoader_Gecko = nullptr;
   gCSSLoader_Servo = nullptr;
-  MOZ_ASSERT(!gStyleCache_Gecko || !gUserContentSheetURL_Gecko,
-             "Got the URL but never used by Gecko?");
-  MOZ_ASSERT(!gStyleCache_Servo || !gUserContentSheetURL_Servo,
-             "Got the URL but never used by Servo?");
+  NS_WARNING_ASSERTION(!gStyleCache_Gecko || !gUserContentSheetURL_Gecko,
+                       "Got the URL but never used by Gecko?");
+  NS_WARNING_ASSERTION(!gStyleCache_Servo || !gUserContentSheetURL_Servo,
+                       "Got the URL but never used by Servo?");
   gStyleCache_Gecko = nullptr;
   gStyleCache_Servo = nullptr;
   gUserContentSheetURL_Gecko = nullptr;
   gUserContentSheetURL_Servo = nullptr;
 }
 
 void
 nsLayoutStylesheetCache::SetUserContentCSSURL(nsIURI* aURI)