I'm using Firefox 59.0b5/64 bit on Win 10. On a new project, DevTools isn't recognizing the CSS sourcemap created with gulp-sourcemap. Sourcemaps created on earlier projects work fine in Firefox so I don't believe it's a Firefox settings issue, and sourcemaps in Chrome DevTools work fine on this project, so gulp-sourcemap seems to be working.
Is there a way to see what's going on under the hood so I can troubleshoot this problem? I suspect there's a glitch in the sourcemap that breaks Firefox devtools but I don't know how to find it.
The slightest clue would be appreciated.