Sass and Less are expressive languages that compile into CSS. If you’re using Sass or Less to generate your CSS, you might want to debug the source that you authored and not the generated CSS. Luckily you can now do this in the Firefox 29 developer tools using source maps. The Firefox developer tools use source maps to show the line number of rules in the original source, and let you edit original
![Live Editing Sass and Less in the Firefox Developer Tools – Mozilla Hacks - the Web developer blog](https://cdn-ak-scissors.b.st-hatena.com/image/square/8f043099b608abf8384b24171faa177d3698e62e/height=288;version=1;width=512/https%3A%2F%2Fhacks.mozilla.org%2Fwp-content%2Fthemes%2FHax%2Fimg%2Fhacks-meta-image.jpg)