Welcome to Firefox Developer Edition
Debugger
Powerful JavaScript debugger with support for your framework.
Storage panel
Add, modify and remove cache, cookies, databases and session data.
Responsive Design Mode
Test sites on emulated devices in your browser.
Performance
Unblock bottlenecks, streamline processes, optimize assets.
Style Editor
Edit and manage all your CSS stylesheets in your browser.
Inactive CSS
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.
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Firefox DevTools
The new Firefox DevTools are powerful, flexible, and best of all, hackable. This includes a best-in-class JavaScript debugger, which can target multiple browsers and is built in React and Redux.
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Master CSS Grid
Firefox is the only browser with tools built specifically for building and designing with CSS Grid. These tools allow you to visualize the grid, display associated area names, preview transformations on the grid and much more.
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Fonts Panel
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.
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Speak up
Feedback makes us better. Tell us how we can improve the browser and Developer tools.
Get involved
Help build the last independent browser. Write code, fix bugs, make add-ons, and more.