Developer Edition enables a number of features not currently available for regular Firefox. The two major ones are build time features which can't be enabled in other releases (besides Nightly). One build feature is Unsigned Add-ons, which allows for add-on development where it isn't possible otherwise. The other is Async JavaScript callstacks which are very useful to capture but tend to slow down regular browsing otherwise. Besides build features there a lot of prefs we turn on to make development easier. If you try using Chrome or Firefox release with DevTools you will need to do something extra to be able to "paste into the console" (something that prevents people on facebook from owning themselves) and that guard isn't on by default in Developer Edition. [I'm the Product Manger for Firefox DevTools]