Breaking Change: -moz-document

Firefox used to have a @-moz-document rule requiring special parsing. As support is removed from Firefox, Sass is in the process of removing support for parsing them.

Sass has historically supported a special parsing for the @-moz-document rule. As Firefox dropped support for them, Sass will also drop support for the special parsing and will treat it as an unknown at-rule.

There is one exception: an empty url prefix function is still allowed, as that’s used in a hack targetting Firefox.

SCSS
Sass
CSS
SCSS Syntax@-moz-document url-prefix() {
  .error {
    color: red;
  }
}
Sass Syntax@-moz-document url-prefix()
  .error
    color: red


CSS Output@-moz-document url-prefix() {
  .error {
    color: red;
  }
}

Transition Period permalinkTransition Period

Dart Sass: since 1.7.2
LibSass: ✗
Ruby Sass: ✗

First, we’ll emit deprecation warnings for all usages of @-moz-document except for the empty url-prefix hack.

In Dart Sass 2.0, @-moz-document will be treated as an unknown at-rule.