Merge pull request #11526 from erikflowers/firefox-placeholder-fix

Firefox placeholder text is faded out and not the full color. 

less/mixins.less

@@ -55,7 +55,7 @@
 // Placeholder text
 .placeholder(@color: @input-color-placeholder) {
   &:-moz-placeholder            { color: @color; } // Firefox 4-18
-  &::-moz-placeholder           { color: @color; } // Firefox 19+
+  &::-moz-placeholder           { color: @color; opacity:1; } // Firefox 19+
   &:-ms-input-placeholder       { color: @color; } // Internet Explorer 10+
   &::-webkit-input-placeholder  { color: @color; } // Safari and Chrome
 }