The Tor Browser / file revision

 function test() {

   let osString = Cc["@mozilla.org/xre/app-info;1"].

                  getService(Ci.nsIXULRuntime).OS;

   // this test is Linux-specific

   if (osString != "Linux")

     return;

   let shell = Cc["@mozilla.org/browser/shell-service;1"].

               getService(Ci.nsIShellService);

   shell.setDefaultBrowser(true, false);

   ok(shell.isDefaultBrowser(true, false), "we got here and are the default browser");

   ok(shell.isDefaultBrowser(true, true), "we got here and are the default browser");

 }