--- a/dom/xul/nsXULPrototypeCache.cpp
+++ b/dom/xul/nsXULPrototypeCache.cpp
@@ -502,17 +502,17 @@ nsXULPrototypeCache::BeginCaching(nsIURI
 
     // Get the chrome directory to validate against the one stored in the
     // cache file, or to store there if we're generating a new file.
     nsCOMPtr<nsIFile> chromeDir;
     rv = NS_GetSpecialDirectory(NS_APP_CHROME_DIR, getter_AddRefs(chromeDir));
     if (NS_FAILED(rv))
         return rv;
     nsAutoCString chromePath;
-    rv = chromeDir->GetNativePath(chromePath);
+    rv = chromeDir->GetPersistentDescriptor(chromePath);
     if (NS_FAILED(rv))
         return rv;
 
     // XXXbe we assume the first package's locale is the same as the locale of
     // all subsequent packages of cached chrome URIs....
     nsAutoCString package;
     rv = aURI->GetHost(package);
     if (NS_FAILED(rv))