Merge branch 'master' into pr/12412

Conflicts:
	dist/css/bootstrap-theme.css.map
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
	docs/assets/js/customize.min.js
	docs/assets/js/raw-files.min.js
	docs/dist/css/bootstrap-theme.css.map
	docs/dist/css/bootstrap.css.map
	docs/dist/css/bootstrap.min.css
	test-infra/npm-shrinkwrap.canonical.json

less/mixins.less

@@ -54,8 +54,7 @@
 
 // Placeholder text
 .placeholder(@color: @input-color-placeholder) {
-  &:-moz-placeholder            { color: @color; } // Firefox 4-18
-  &::-moz-placeholder           { color: @color;   // Firefox 19+
+  &::-moz-placeholder           { color: @color;   // Firefox
                                   opacity: 1; } // See https://github.com/twbs/bootstrap/pull/11526
   &:-ms-input-placeholder       { color: @color; } // Internet Explorer 10+
   &::-webkit-input-placeholder  { color: @color; } // Safari and Chrome
@@ -253,7 +252,6 @@
   -webkit-user-select: @select;
      -moz-user-select: @select;
       -ms-user-select: @select; // IE10+
-       -o-user-select: @select;
           user-select: @select;
 }
 
@@ -629,10 +627,7 @@
 }
 
 .responsive-invisibility() {
-    &,
-  tr&,
-  th&,
-  td& { display: none !important; }
+  display: none !important;
 }
 
 
@@ -927,7 +922,8 @@
     line-height: @input-height;
   }
 
-  textarea& {
+  textarea&,
+  select[multiple]& {
     height: auto;
   }
 }