diff --git a/content/base/src/nsDOMFile.cpp b/content/base/src/nsDOMFile.cpp
index 82c28859be3a..1a6077b17e0a 100644
--- a/content/base/src/nsDOMFile.cpp
+++ b/content/base/src/nsDOMFile.cpp
@@ -629,32 +629,51 @@ nsDOMFile::Initialize(nsISupports* aOwner,
                       PRUint32 aArgc,
                       jsval* aArgv)
 {
+  nsresult rv;
+
   if (!nsContentUtils::IsCallerChrome()) {
     return NS_ERROR_DOM_SECURITY_ERR; // Real short trip
   }
 
   NS_ENSURE_TRUE(aArgc > 0, NS_ERROR_UNEXPECTED);
 
-  // We expect to get a path to represent as a File object
-  if (!JSVAL_IS_STRING(aArgv[0]))
-    return NS_ERROR_UNEXPECTED;
+  // We expect to get a path to represent as a File object,
+  // or an nsIFile
+  nsCOMPtr<nsIFile> file;
+  if (!JSVAL_IS_STRING(aArgv[0])) {
+    // Lets see if it's an nsIFile
+    if (!JSVAL_IS_OBJECT(aArgv[0])) {
+      return NS_ERROR_UNEXPECTED; // We're not interested
+    }
 
-  JSString* str = JS_ValueToString(aCx, aArgv[0]);
-  NS_ENSURE_TRUE(str, NS_ERROR_XPC_BAD_CONVERT_JS);
+    JSObject* obj = JSVAL_TO_OBJECT(aArgv[0]);
+    NS_ASSERTION(obj, "This is a bit odd");
 
-  nsDependentJSString xpcomStr;
-  if (!xpcomStr.init(aCx, str)) {
-    return NS_ERROR_XPC_BAD_CONVERT_JS;
+    // Is it an nsIFile
+    file = do_QueryInterface(
+      nsContentUtils::XPConnect()->
+        GetNativeOfWrapper(aCx, obj));
+    if (!file)
+      return NS_ERROR_UNEXPECTED;
+  } else {
+    // It's a string
+    JSString* str = JS_ValueToString(aCx, aArgv[0]);
+    NS_ENSURE_TRUE(str, NS_ERROR_XPC_BAD_CONVERT_JS);
+
+    nsDependentJSString xpcomStr;
+    if (!xpcomStr.init(aCx, str)) {
+      return NS_ERROR_XPC_BAD_CONVERT_JS;
+    }
+
+    nsCOMPtr<nsILocalFile> localFile;
+    nsresult rv = NS_NewLocalFile(xpcomStr,
+                                  PR_FALSE, getter_AddRefs(localFile));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    file = do_QueryInterface(localFile);
+    NS_ASSERTION(file, "This should never happen");
   }
 
-  nsCOMPtr<nsILocalFile> localFile;
-  nsresult rv = NS_NewLocalFile(xpcomStr,
-                                PR_FALSE, getter_AddRefs(localFile));
-  NS_ENSURE_SUCCESS(rv, rv);
-
-  nsCOMPtr<nsIFile> file = do_QueryInterface(localFile, &rv);
-  NS_ENSURE_SUCCESS(rv, rv);
-
   PRBool exists;
   rv = file->Exists(&exists);
   NS_ENSURE_SUCCESS(rv, rv);
diff --git a/content/base/test/chrome/test_fileconstructor.xul b/content/base/test/chrome/test_fileconstructor.xul
index 9fe58716241f..9c916358a16f 100644
--- a/content/base/test/chrome/test_fileconstructor.xul
+++ b/content/base/test/chrome/test_fileconstructor.xul
@@ -45,10 +45,13 @@ file.append("test");
 file.append("chrome");
 file.append("fileconstructor_file.png");
 
-var domfile = new File(file.path);
-ok(domfile instanceof File, "File() should return a File");
-is(domfile.type, "image/png", "File should be a PNG");
-is(domfile.size, 95, "File has size 95 (and more importantly we can read it)");
+doTest(new File(file.path));
+doTest(new File(file));
+function doTest(domfile) {
+  ok(domfile instanceof File, "File() should return a File");
+  is(domfile.type, "image/png", "File should be a PNG");
+  is(domfile.size, 95, "File has size 95 (and more importantly we can read it)");
+}
 
 try {
   var boomfile = new File();