$placeholders: '-webkit-input-placeholder',

'-moz-placeholder',
'-ms-input-placeholder';

@mixin placeholder {

@each $placeholder in $placeholders {
  @if $placeholder == "-webkit-input-placeholder" {
    &::#{$placeholder} {
      @content;
    }
  }
  @else if $placeholder == "-moz-placeholder" {
    // FF 18-
    &:#{$placeholder} {
      @content;
    }

    // FF 19+
    &::#{$placeholder} {
      @content;
    }
  }
  @else {
    &:#{$placeholder} {
      @content;
    }
  }
}

}