If you work in an environment that has multiple versions of Internet Explorer and trying to support SharePoint 2013, you will need to add a simple HTML tag to your master page/custom master page in order to be truly backwards compatible especially if you have IE 8 or IE 9 in your environment.
Place this tag in your <head></head> section in your start page.
<meta http-equiv=”x-ua-compatible” content=”ie=edge”>
This will help with forward and backwards compatibility.
Please TEST in your test/development environment(s) first before applying to your production site.