Perhaps the biggest change in Firefox 15 is that it ships with a debugger that developers can use to find issues with their JavaScript code. The debugger is available via the Web Developer menu.

There’s also a new JavaScript Debugger that developers can use over a local network to remotely debug apps running on Firefox for Android, for example.

Specifically, Web devs will be able to use Firefox's JavaScript debugger, DOM inspector, and CSS editor with Firefox, Chrome, and Safari.