--- a/dom/bindings/GenerateCSS2PropertiesWebIDL.py
+++ b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
@@ -1,64 +1,75 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import sys
 import string
+import argparse
 
 # Generates a line of WebIDL with the given spelling of the property name
 # (whether camelCase, _underscorePrefixed, etc.) and the given array of
 # extended attributes.
 def generateLine(propName, extendedAttrs):
     return "  [%s] attribute DOMString %s;\n" % (", ".join(extendedAttrs),
                                                  propName)
-propList = eval(sys.stdin.read())
-props = ""
-for [name, prop, id, flags, pref, proptype] in propList:
-    if "CSS_PROPERTY_INTERNAL" in flags:
-        continue
-    # Unfortunately, even some of the getters here are fallible
-    # (e.g. on nsComputedDOMStyle).
-    extendedAttrs = ["Throws", "TreatNullAs=EmptyString"]
-    if pref is not "":
-        extendedAttrs.append('Pref="%s"' % pref)
+def generate(output, idlFilename):
+    propList = eval(sys.stdin.read())
+    props = ""
+    for [name, prop, id, flags, pref, proptype] in propList:
+        if "CSS_PROPERTY_INTERNAL" in flags:
+            continue
+        # Unfortunately, even some of the getters here are fallible
+        # (e.g. on nsComputedDOMStyle).
+        extendedAttrs = ["Throws", "TreatNullAs=EmptyString"]
+        if pref is not "":
+            extendedAttrs.append('Pref="%s"' % pref)
 
-    # webkit properties get a capitalized "WebkitFoo" accessor (added here)
-    # as well as a camelcase "webkitFoo" accessor (added next).
-    if (prop.startswith("Webkit")):
+        # webkit properties get a capitalized "WebkitFoo" accessor (added here)
+        # as well as a camelcase "webkitFoo" accessor (added next).
+        if (prop.startswith("Webkit")):
+            props += generateLine(prop, extendedAttrs)
+
+        # Generate a line with camelCase spelling of property-name (or capitalized,
+        # for Moz-prefixed properties):
+        if not prop.startswith("Moz"):
+            prop = prop[0].lower() + prop[1:]
         props += generateLine(prop, extendedAttrs)
 
-    # Generate a line with camelCase spelling of property-name (or capitalized,
-    # for Moz-prefixed properties):
-    if not prop.startswith("Moz"):
-        prop = prop[0].lower() + prop[1:]
-    props += generateLine(prop, extendedAttrs)
-
-    # Per spec, what's actually supposed to happen here is that we're supposed
-    # to have properties for:
-    #
-    # 1) Each supported CSS property name, camelCased.
-    # 2) Each supported name that contains dashes but doesn't start with a
-    #    dash, without any changes to the name.
-    # 3) cssFloat
-    #
-    # Note that "float" will cause a property called "float" to exist due to (1)
-    # in that list.
-    #
-    # In practice, cssFloat is the only case in which "name" doesn't contain
-    # "-" but also doesn't match "prop".  So the above generatePropLine() call
-    # covered (3) and all of (1) except "float".  If we now output attributes
-    # for all the cases where "name" doesn't match "prop" and "name" doesn't
-    # start with "-", that will cover "float" and (2).
-    if prop != name and name[0] != "-":
-        extendedAttrs.append('BinaryName="%s"' % prop)
-        # Throw in a '_' before the attribute name, because some of these
-        # property names collide with IDL reserved words.
-        props += generateLine("_" + name, extendedAttrs)
+        # Per spec, what's actually supposed to happen here is that we're supposed
+        # to have properties for:
+        #
+        # 1) Each supported CSS property name, camelCased.
+        # 2) Each supported name that contains dashes but doesn't start with a
+        #    dash, without any changes to the name.
+        # 3) cssFloat
+        #
+        # Note that "float" will cause a property called "float" to exist due to (1)
+        # in that list.
+        #
+        # In practice, cssFloat is the only case in which "name" doesn't contain
+        # "-" but also doesn't match "prop".  So the above generatePropLine() call
+        # covered (3) and all of (1) except "float".  If we now output attributes
+        # for all the cases where "name" doesn't match "prop" and "name" doesn't
+        # start with "-", that will cover "float" and (2).
+        if prop != name and name[0] != "-":
+            extendedAttrs.append('BinaryName="%s"' % prop)
+            # Throw in a '_' before the attribute name, because some of these
+            # property names collide with IDL reserved words.
+            props += generateLine("_" + name, extendedAttrs)
 
 
-idlFile = open(sys.argv[1], "r")
-idlTemplate = idlFile.read()
-idlFile.close()
+    idlFile = open(idlFilename, "r")
+    idlTemplate = idlFile.read()
+    idlFile.close()
+
+    output.write("/* THIS IS AN AUTOGENERATED FILE.  DO NOT EDIT */\n\n" +
+                 string.Template(idlTemplate).substitute({"props": props}) + '\n')
 
-print ("/* THIS IS AN AUTOGENERATED FILE.  DO NOT EDIT */\n\n" +
-       string.Template(idlTemplate).substitute({"props": props}))
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('idlFilename', help='IDL property file template')
+    args = parser.parse_args()
+    generate(sys.stdout, args.idlFilename)
+
+if __name__ == '__main__':
+    main()