User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20171024165158 Steps to reproduce: Normal use of Firefox Developer Edition 58.0b1 (64.bit) using the HTML/CSS inspector. It can't find my SCSS files however regular Firefox 56.0.2 (64-bit) can. Actual results: Console log report: Source map error: request failed with status 401 Resource URL: https://192.168.0.4/dev/css/admin.css Source Map URL: admin.css.map Expected results: It should be able to find scss files via admin.css.map

Based on the 401, I would guess this is maybe a dup of bug 1404245. Are you using some kind of auth for these URLs? Also, maybe looking in the browser (not web) console would show something about the source-map network request.

Please see Tom's questions above (note that the browser console can be opened with ctrl+shift+J).

Since there hasn't been any response for 6 months, I am gonna flag this as a dupe of bug 1404245