diff --git a/less/mixins.less b/less/mixins.less
index 50ccafa7c0..e76d8d697d 100644
--- a/less/mixins.less
+++ b/less/mixins.less
@@ -55,7 +55,8 @@
 // Placeholder text
 .placeholder(@color: @input-color-placeholder) {
   &:-moz-placeholder            { color: @color; } // Firefox 4-18
-  &::-moz-placeholder           { color: @color; opacity:1; } // Firefox 19+
+  &::-moz-placeholder           { color: @color;   // Firefox 19+
+                                  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
 }