Quill follows the lead of many other open source libraries of supporting the latest two browser versions. IE9 and IE10 control fewer than 1% of the browser market and Microsoft itself has ended support. Quill will not be supporting IE9 or IE10.
Will you make adjustments to work on IE 11 ? I've tested it in IE Edge and it is working nicely, but IE11 unfortunately not. There is issue where IE11 doesn't support 'classList' - this is easy modification
@fpavlic IE11 is supported and there is a polyfill already included to handle the classList case. Please file a bug report for each issue you are encountering with IE11 and please follow the bug report instructions.