Komodo Edit
Overview
Komodo Edit is a free, open source IDE written in Python and based on the Mozilla platform, the same framework which runs Firefox so it should feel familiar as soon as you start using it.
Its features include excellent file and project management, custom editor setups, keyboard shortcuts, programmable macros, templates, autocomplete, function and property hyperlinking, excellent search and replace, and a host of addons.
What sets Komodo apart from other editors (from a JSFL perspective) is the xJSFL extension that ships with xJSFL, providing full JSFL autocomplete, as well as macros, publishing shortcuts and templates to get you writing and running JSFL and xJSFL code in no time at all.
With Komodo you write fully-auto-completed code in minutes, and run it in seconds using the handy CTRL+Enter shortcut, just like Flash.