[disabled] => :disabled

:disabled is supported in IE9+ and all modern browsers

scss/_buttons.scss

@@ -43,7 +43,7 @@
   }
 
   &.disabled,
-  &[disabled],
+  &:disabled,
   fieldset[disabled] & {
     pointer-events: none; // Future-proof disabling of clicks
     cursor: $cursor-disabled;
@@ -88,7 +88,7 @@
   &,
   &:active,
   &.active,
-  &[disabled],
+  &:disabled,
   fieldset[disabled] & {
     background-color: transparent;
     @include box-shadow(none);
@@ -105,7 +105,7 @@
     text-decoration: underline;
     background-color: transparent;
   }
-  &[disabled],
+  &:disabled,
   fieldset[disabled] & {
     &:hover,
     &:focus {

scss/_forms.scss

@@ -140,7 +140,7 @@ output {
   // HTML5 says that controls under a fieldset > legend:first-child won't be
   // disabled if the fieldset is disabled. Due to implementation difficulty, we
   // don't honor that edge case; we style them as disabled anyway.
-  &[disabled],
+  &:disabled,
   &[readonly],
   fieldset[disabled] & {
     cursor: $cursor-disabled;
@@ -263,7 +263,7 @@ input[type="search"] {
 // Note: Neither radios nor checkboxes can be readonly.
 input[type="radio"],
 input[type="checkbox"] {
-  &[disabled],
+  &:disabled,
   &.disabled,
   fieldset[disabled] & {
     cursor: $cursor-disabled;

scss/_navbar.scss

@@ -309,7 +309,7 @@
     &:focus {
       color: $navbar-default-link-hover-color;
     }
-    &[disabled],
+    &:disabled,
     fieldset[disabled] & {
       &:hover,
       &:focus {
@@ -422,7 +422,7 @@
       color: $navbar-inverse-link-hover-color;
     }
 
-    &[disabled],
+    &:disabled,
     fieldset[disabled] & {
       &:hover,
       &:focus {

scss/mixins/_buttons.scss

@@ -28,7 +28,7 @@
     @include box-shadow(inset 0 3px 5px rgba(0,0,0,.125));
   }
   &.disabled,
-  &[disabled],
+  &:disabled,
   fieldset[disabled] & {
     &,
     &:hover,