Mozilla has been steadily improving its MDN Web Docs and Firefox Developer Tools. The latest version of Firefox, version 70, combines both resources into a webmaster resource for identifying and fixing CSS that isn’t being used or is broken.
Webmasters can now debug CSS in Firefox and find properties that are inactive or have errors with its values. It supports most CSS properties, including
If the tool finds an inactive property, it will turn it gray and append it with an information icon ℹ️. Hovering over the icon displays details about the issue and also provides a link to the related MDN Web Doc. The tool will also highlight if the syntax is incorrect by displaying a warning icon ⚠️.
Miriam Suzanne, Web Developer at Mozilla, explains how the new feature works in Firefox Developer Tools.
Firefox 70 is available starting October 22, 2019 from Mozilla’s Firefox download page.