So far we plan to use Vim to write the code, no fancy IDE. For generating output we would use Spidermonkey's shell environment. JSLint could serve as a moderate syntax checking tool.
If we are already on the right track, then maybe you can supply us with a few tips and tricks. It seems like you have a development environment planned already. So what exactly are you looking for? A way to check that your code will run in IE, Firefox, Safari, Opera, Konqueror and Chrome?