Cu.importGlobalProperties(["File"]); var testFile = Cc["@mozilla.org/file/directory_service;1"] .getService(Ci.nsIDirectoryService) .QueryInterface(Ci.nsIProperties) .get("ProfD", Ci.nsIFile); testFile.append("prefs.js"); addMessageListener("file.open", function () { File.createFromNsIFile(testFile).then(function(file) { File.createFromNsIFile(testFile, { lastModified: 123 }).then(function(fileWithDate) { sendAsyncMessage("file.opened", { file, mtime: testFile.lastModifiedTime, fileWithDate, fileDate: 123, }); }); }); });