Firefox Developer Edition features the latest changes and development tools you need to build for the web. Available for Windows, Linux, and Mac.
The beautiful thing about the developer edition is that anyone can use and test it. Of course, you don't want to use this as a daily browser, especially in work situations.
Otherwise, we enjoyed using the new Firefox so much; we might consider switching back.
Firefox Quantum Developer Edition focuses on the new CSS engine designed to be the fastest, most powerful Firefox to date. Of course, since it is the developer version, the features focused on are for developers, including:
Inspector allows you to inspect and refine code to build pixel-perfect layouts.
Monitor network requests that can slow or block your site.
Add, modify and remove cache, cookies, databases, and session data.