Add conditional stylesheet CSS for internet explorer only The following methods can be used to add CSS for specific versions of IE:


Paste the code into html.tpl.php:

&lt;!--[if lt IE 9]&gt;&lt;link type="text/css" rel="stylesheet" src="/sites/all/themes/mytheme/less/ie.css"&gt;&lt;![endif]--&gt;
Make use of the plugin Conditional Styles
Use drupal_add_css() function


I have always used option #1 above, and adding yet another plugin for something so simple seemed crazy. BUT working with LESS and calling in statically means the file does not get processed by the LESS pre-processor, so the question:

How do you include a stylesheet using drupal_add_css() for specific versions of IE?
I Found the solution in the comments on the drupal documentation for drupal_add_css():

drupal_add_css(
  path_to_theme() . '/less/ie.less',
  array(
    'browsers' =&gt; array(
      'IE' =&gt; 'lte IE 9',
      '!IE' =&gt; FALSE
    )
  )
);


Using this resulted in the LESS file being compiled by the LESS pre-processor, and the style was included within &lt;!--[if lte IE 9]&gt; comment tags.