SpiderMonkey JavaScript Shell SpiderMonkey is the JavaScript engine used in Firefox 2.0. On this page, you can download the SpiderMonkey engine as a stand-alone JavaScript shell. Download SpiderMonkey for Windows: To download the JavaScript shell, download the SpiderMonkey executable and the Cygwin DLL to the same folder. SpiderMonkey executable Cygwin DLL Download SpiderMonkey for Mac OS X: To do