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 , then +Customize and click Use Firefox Developer Edition theme 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.