diff -r 000000000000 -r 6474c204b198 dom/bindings/parser/tests/test_deduplicate.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/parser/tests/test_deduplicate.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,15 @@
+import WebIDL
+
+def WebIDLTest(parser, harness):
+    parser.parse("""
+        interface Foo;
+        interface Bar;
+        interface Foo;
+        """);
+
+    results = parser.finish()
+
+    # There should be no duplicate interfaces in the result.
+    expectedNames = sorted(['Foo', 'Bar'])
+    actualNames = sorted(map(lambda iface: iface.identifier.name, results))
+    harness.check(actualNames, expectedNames, "Parser shouldn't output duplicate names.")