The Tor Browser / file revision

 let ioService = Cc["@mozilla.org/network/io-service;1"]

                 .getService(Ci.nsIIOService);

 let resProt = ioService.getProtocolHandler("resource")

               .QueryInterface(Ci.nsIResProtocolHandler);

 function run_test() {

     // Define a resource:// alias that points to another resource:// URI.

     let greModulesURI = ioService.newURI("resource://gre/modules/", null, null);

     resProt.setSubstitution("my-gre-modules", greModulesURI);

     // When we ask for the alias, we should not get the resource://

     // URI that we registered it for but the original file URI.

     let greFileSpec = ioService.newURI("modules/", null,

                                        resProt.getSubstitution("gre")).spec;

     let aliasURI = resProt.getSubstitution("my-gre-modules");

     do_check_eq(aliasURI.spec, greFileSpec);

     // Resolving URIs using the original resource path and the alias

     // should yield the same result.

     let greNetUtilURI = ioService.newURI("resource://gre/modules/NetUtil.jsm",

                                          null, null);

     let myNetUtilURI = ioService.newURI("resource://my-gre-modules/NetUtil.jsm",

                                         null, null);

     do_check_eq(resProt.resolveURI(greNetUtilURI),

                 resProt.resolveURI(myNetUtilURI));

 }