diff --git a/dist/css/bootstrap-theme.css.map b/dist/css/bootstrap-theme.css.map
index 016a8dabc448d83afc1bd12818684a5e1e2434ee..7622d7d8514c0453907adfe6d4bccae0a7d7d83b 100644
Binary files a/dist/css/bootstrap-theme.css.map and b/dist/css/bootstrap-theme.css.map differ
diff --git a/dist/css/bootstrap.css.map b/dist/css/bootstrap.css.map
index f2e3f2ddaaaf569ea7a2caa084ed51acc3050b98..21668ab3ef5768612714d409c92f5b8367c096cc 100644
Binary files a/dist/css/bootstrap.css.map and b/dist/css/bootstrap.css.map differ
diff --git a/docs/_includes/components/thumbnails.html b/docs/_includes/components/thumbnails.html
index b41fef72e0db02ac95b3551704ce25bf22cb3b27..766d79f36522f74044e16c46797b567ac2d77371 100644
--- a/docs/_includes/components/thumbnails.html
+++ b/docs/_includes/components/thumbnails.html
@@ -33,7 +33,7 @@
 <div class="row">
   <div class="col-xs-6 col-md-3">
     <a href="#" class="thumbnail">
-      <img data-src="holder.js/100%x180" alt="...">
+      <img src="..." alt="...">
     </a>
   </div>
   ...
@@ -80,7 +80,7 @@
 <div class="row">
   <div class="col-sm-6 col-md-4">
     <div class="thumbnail">
-      <img data-src="holder.js/300x300" alt="...">
+      <img src="..." alt="...">
       <div class="caption">
         <h3>Thumbnail label</h3>
         <p>...</p>
diff --git a/less/carousel.less b/less/carousel.less
index a28e397a551d8569fd9fc1f3e86d75ded2e27b56..4bbe946d3aa8f36a49c9dd77306e02888634be87 100644
--- a/less/carousel.less
+++ b/less/carousel.less
@@ -196,6 +196,7 @@
     // Internet Explorer 8-9 does not support clicks on elements without a set
     // `background-color`. We cannot use `filter` since that's not viewed as a
     // background color by the browser. Thus, a hack is needed.
+    // See https://developer.mozilla.org/en-US/docs/Web/Events/click#Internet_Explorer
     //
     // For IE8, we set solid black as it doesn't support `rgba()`. For IE9, we
     // set alpha transparency for the best results possible.
diff --git a/less/close.less b/less/close.less
index 9b4e74f2b82f8fb183bdd9a5a5ddae4ec29deb92..6d5bfe087aed3342270b1de9d70d034c474a3779 100644
--- a/less/close.less
+++ b/less/close.less
@@ -23,6 +23,7 @@
   // Additional properties for button version
   // iOS requires the button element instead of an anchor tag.
   // If you want the anchor version, it requires `href="#"`.
+  // See https://developer.mozilla.org/en-US/docs/Web/Events/click#Safari_Mobile
   button& {
     padding: 0;
     cursor: pointer;
diff --git a/less/forms.less b/less/forms.less
index d2ea45036df2c348de220eea2a5acc0136ad43f0..bf15cc8a9e14c83f9e35f35ab4b8df0a35590692 100644
--- a/less/forms.less
+++ b/less/forms.less
@@ -143,7 +143,7 @@ output {
   fieldset[disabled] & {
     cursor: @cursor-disabled;
     background-color: @input-bg-disabled;
-    opacity: 1; // iOS fix for unreadable disabled content
+    opacity: 1; // iOS fix for unreadable disabled content; see https://github.com/twbs/bootstrap/issues/11655
   }
 
   // Reset height for `textarea`s
diff --git a/less/mixins/vendor-prefixes.less b/less/mixins/vendor-prefixes.less
index 31f8e2f7ab1e1aa7cef64d60602dba8a54892d7c..afd3331c31da856f226b354916e21ebad9d3311a 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
diff --git a/less/tables.less b/less/tables.less
index ba24498a3942e1d4f9c95fa28363aa9ee223b6fa..3c801aedbbe1b0c8b8a0df87550fa1aacc66ca1c 100644
--- a/less/tables.less
+++ b/less/tables.less
@@ -133,7 +133,7 @@ th {
 // Reset default table behavior
 
 table col[class*="col-"] {
-  position: static; // Prevent border hiding in Firefox and IE9/10 (see https://github.com/twbs/bootstrap/issues/11623)
+  position: static; // Prevent border hiding in Firefox and IE9-11 (see https://github.com/twbs/bootstrap/issues/11623)
   float: none;
   display: table-column;
 }
@@ -141,7 +141,7 @@ table {
   td,
   th {
     &[class*="col-"] {
-      position: static; // Prevent border hiding in Firefox and IE9/10 (see https://github.com/twbs/bootstrap/issues/11623)
+      position: static; // Prevent border hiding in Firefox and IE9-11 (see https://github.com/twbs/bootstrap/issues/11623)
       float: none;
       display: table-cell;
     }
diff --git a/less/theme.less b/less/theme.less
index a15d16ecd2d2c1167c1027d6fa26485f3c592ad7..3673accc0999596e2d285f2adacce602146345fa 100644
--- a/less/theme.less
+++ b/less/theme.less
@@ -36,7 +36,7 @@
 // Mixin for generating new styles
 .btn-styles(@btn-color: #555) {
   #gradient > .vertical(@start-color: @btn-color; @end-color: darken(@btn-color, 12%));
-  .reset-filter(); // Disable gradients for IE9 because filter bleeds through rounded corners
+  .reset-filter(); // Disable gradients for IE9 because filter bleeds through rounded corners; see https://github.com/twbs/bootstrap/issues/10620
   background-repeat: repeat-x;
   border-color: darken(@btn-color, 14%);
 
@@ -130,7 +130,7 @@
 // Inverted navbar
 .navbar-inverse {
   #gradient > .vertical(@start-color: lighten(@navbar-inverse-bg, 10%); @end-color: @navbar-inverse-bg);
-  .reset-filter(); // Remove gradient in IE<10 to fix bug where dropdowns don't get triggered
+  .reset-filter(); // Remove gradient in IE<10 to fix bug where dropdowns don't get triggered; see https://github.com/twbs/bootstrap/issues/10257
 
   .navbar-nav > .open > a,
   .navbar-nav > .active > a {