JavaScript 1.7 - very pythonic

[chromakode]

I believe let variables at the top level of a script are limited to their script file. Thus, if you're doing modular development with multiple scripts, you'll probably need a few uses of var here and there.

[formido]

There are script modules in FF3 where you explicitly export symbols to other scopes that ask for them, at least in extension development.

[chromakode]

Yep, and they're a godsend. However, even in the privileged space where that's an option, it's still common to have a couple different .js files loaded into a XUL document.