http://jimmy.schementi.com/silverlight/Chiron.zip This contains Chiron.exe, the Silverlight development web server for Dynamic Languages, with a fix for the IPv4/6 issues. Let me know if anyone has issues on Firefox on either Windows or Mac. This fix will appear on Codeplex in a week. I haven't fixed the "file:///" bug on the Mac yet since it doesn't repro on Windows ... so it probably (?) is a Mono bug. I'll see if I can work around it, but in the meantime you can just do "Chiron /m /d:app" to generate the AppManifest.xaml to disk ... then you can edit it and remove the "file://"s (leave one "/" in the front though!). More information about the issue To understand the bug a little more, Chiron currently tries to listen on IPv6 first, and if that fails it then tries to listen on IPv4. While that’s a fine solution for Vista/XP/Mac, as well as browsers that are tied to their operating system’s network settings (IE, Safari), it’s a problem for browsers that support both in some configurable manner (Firefox). The new behavior is to listen on both IPv6 and IPv4 when it can, but not fail if IPv6 fails. This will work on both IPv6/v4 operating systems (so Vista/XP/Mac will both work), as well as v4/v6 configurable browsers (Firefox), no matter what their settings. In the future Along other Chiron news, I’m also planning on removing the “only works on localhost” constraint. I don’t think it’ll be difficult, but I just need to find hacking time. =) I find it useful because I’d like to do development on one machine and browser to it with another machine, especially if I’m testing different browsers. Would others find it useful as well?