fix #2846: Firefox required two clicks on selects to get to options dropdown

docs/assets/css/bootstrap.css

@@ -991,6 +991,7 @@ select:focus:required:invalid:focus {
 .input-append select,
 .input-prepend .uneditable-input,
 .input-append .uneditable-input {
+  position: relative;
   margin-bottom: 0;
   *margin-left: 0;
   vertical-align: middle;
@@ -1004,7 +1005,6 @@ select:focus:required:invalid:focus {
 .input-append select:focus,
 .input-prepend .uneditable-input:focus,
 .input-append .uneditable-input:focus {
-  position: relative;
   z-index: 2;
 }
 .input-prepend .uneditable-input,

less/forms.less

@@ -365,13 +365,13 @@ select:focus:required:invalid {
   input,
   select,
   .uneditable-input {
+    position: relative; // placed here by default so that on :focus we can place the input above the .add-on for full border and box-shadow goodness
     margin-bottom: 0; // prevent bottom margin from screwing up alignment in stacked forms
     *margin-left: 0;
     vertical-align: middle;
     .border-radius(0 3px 3px 0);
     // Make input on top when focused so blue border and shadow always show
     &:focus {
-      position: relative;
       z-index: 2;
     }
   }