I've been building an extension with Kango and so far everything has worked as advertised. The build process is a snap. Everything is written in Javascript; I

I've been building an extension with Kango and so far everything has worked as advertised. The build process is a snap. Everything is written in Javascript; I have complete access to the DOM via Jquery. Builds for FF, Chrome and Opera. And their support has been quite responsive. The only downside is that for IE build support you have to buy a commercial license which isn't cheap ($2500).