Firefox Browser Developer Edition
Welcome to your new favourite browser. Get the latest features, fast performance, and the development tools you need to build for the open web.
Firefox Developer Edition automatically sends feedback to Mozilla. Learn more
A Next-Generation CSS Engine
Firefox Quantum includes a new CSS engine, written in Rust, that has state-of-the-art innovations and is blazingly fast.
Firefox DevTools now grays out CSS declarations that don’t have an effect on the page. When you hover over the info icon, you’ll see a useful message about why the CSS is not being applied, including a hint about how to fix the problem.
Master CSS Grid
Firefox is the only browser with tools built specifically for building and designing with CSS Grid. These tools allow you to visualise the grid, display associated area names, preview transformations on the grid and much more.
The new fonts panel in Firefox DevTools gives developers quick access to all of the information they need about the fonts being used in an element. It also includes valuable information such as the font source, weight, style and more.
Design. Code. Test. Refine.
Build and Perfect your sites
with Firefox DevTools
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.
Responsive Design Mode
Test sites on emulated devices in your browser.
Fine-tune animations, alignment and padding.
Unblock bottlenecks, streamline processes, optimise assets.
Find memory leaks and make your application zippy.
Edit and manage all your CSS stylesheets in your browser.
Feedback makes us better. Tell us how we can improve the browser and Developer tools.
Help build the last independent browser. Write code, fix bugs, make add-ons, and more.