Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.9)
// Compass (v1.0.0.alpha.20)
// ----

%my-font-style {
    font-family: serif;
}
.my-font-style-dotted {
    font-family: serif;
}

::-webkit-input-placeholder {
    @extend %my-font-style;
}
:-moz-placeholder {
    /* this works > font-family: serif; */
    /* this works > @extend .my-font-style-dotted; */
    /* this failed, reset the webkit pseudo classe too */
    @extend %my-font-style;
}
/* Same issue with 
- &::-moz-placeholder
- &:-ms-input-placeholder
*/

SassMeister-output.css

::-webkit-input-placeholder, :-moz-placeholder {
  font-family: serif;
}

.my-font-style-dotted {
  font-family: serif;
}

:-moz-placeholder {
  /* this works > font-family: serif; */
  /* this works > @extend .my-font-style-dotted; */
  /* this failed, reset the webkit pseudo classe too */
}

/* Same issue with 
- &::-moz-placeholder
- &:-ms-input-placeholder
*/