Move btoa polyfill to theme.config.php.

themes/bootstrap3/templates/layout/layout.phtml

@@ -23,8 +23,6 @@
     <?
       // Set global path for Javascript code:
       $this->headScript()->prependScript("path = '" . rtrim($this->url('home'), '/') . "';");
-      // Polyfill btoa
-      $this->headScript()->appendFile('vendor/base64.js', 'text/javascript', array('conditional' => 'lt IE 10'));
 
       // Deal with cart stuff:
       if (!isset($this->renderingError)) {

themes/bootstrap3/theme.config.php

@@ -11,6 +11,7 @@ return array(
         'print.css:print',
     ),
     'js' => array(
+        'vendor/base64.js:lt IE 10', // btoa polyfill
         'vendor/jquery.min.js',
         'vendor/bootstrap.min.js',
         'vendor/bootstrap-accessibility.min.js',