PRBool-to-error-code double conversion. Conversion for AppendElement() happened in nsSupportsArray.h, we don't need to convert the usage here.

content/xul/document/src/nsXULDocument.cpp

@@ -2178,7 +2178,7 @@ XULDocumentImpl::AddContentModelBuilder(nsIRDFContentModelBuilder* aBuilder)
         return rv;
     }
 
-    return mBuilders->AppendElement(aBuilder) ? NS_OK : NS_ERROR_FAILURE;
+    return mBuilders->AppendElement(aBuilder);
 }
 
 NS_IMETHODIMP

rdf/content/src/nsXULDocument.cpp

@@ -2178,7 +2178,7 @@ XULDocumentImpl::AddContentModelBuilder(nsIRDFContentModelBuilder* aBuilder)
         return rv;
     }
 
-    return mBuilders->AppendElement(aBuilder) ? NS_OK : NS_ERROR_FAILURE;
+    return mBuilders->AppendElement(aBuilder);
 }
 
 NS_IMETHODIMP