diff --git a/less/mixins/vendor-prefixes.less b/less/mixins/vendor-prefixes.less
index 31f8e2f7ab..afd3331c31 100644
--- a/less/mixins/vendor-prefixes.less
+++ b/less/mixins/vendor-prefixes.less
@@ -102,7 +102,7 @@
   // Firefox
   &::-moz-placeholder {
     color: @color;
-    opacity: 1; // See https://github.com/twbs/bootstrap/pull/11526
+    opacity: 1; // Override Firefox's unusual default opacity; see https://github.com/twbs/bootstrap/pull/11526
   }
   &:-ms-input-placeholder { color: @color; } // Internet Explorer 10+
   &::-webkit-input-placeholder  { color: @color; } // Safari and Chrome