Firefox Developer Edition integrates all the developer tools you'll need into one package. It is the only browser dedicated to developers.
How do I switch between the Developer Edition and standard themes?
Click the menu button , thenand click to switch between themes.
For more details, see reverting themes on MDN.
Recover lost bookmarks
Firefox Developer Edition will create a new profile if you run it at the same time as Firefox. To keep your bookmarks on both versions, see Recover lost bookmarks on Firefox Developer Edition
How do I learn more about Firefox Developer Edition?
The Mozilla Developer Network is the best place to learn more about Developer Edition. See MDN Developer Edition documentation for more details.