Windows/Mac/Linux: Firefox has always been a great browser for development, and Mozilla has now released Firefox Developer Edition. It's a browser packed with developer-friendly features, such as WebIDE, Valence for cross-browser debugging and responsive design view.
The Firefox Developer edition features plenty of developer tools and extensions built right into the browser. WebIDE is the replacement for App Manager and lets you build fully functioning applications from your browser or Firefox OS device. Responsive Design View lets you see your app or website as you resize it for different platforms, and Valence lets you debug for different browsers, including Chrome and Safari. Other handy tools include Page Inspector, Web Console and Web Audio Editor.
From the looks of it, Firefox Developer Edition was primarily created with the mobile developer in mind, but that doesn't mean you can't create desktop applications.