Wouldn’t it be nice to use html5 and css3 in SharePoint? No problems, there is actually v5 master out there, created by Kyle Schaefer. Or just use h5ml5 and css3 right away in your webparts and pages. But there is a big problem. It doesn’t work in IE9–. One of the issues (even listed by Kyle) is that “save” doesn’t work in modal dialogs where Rich Text Editor is used. Especialy it is for modal dialogs. The problem is not IE9, neither html5 and css3. After some digging in javascript code which is shipped with SharePoint I found out that the problem is some legacy javascript code which is not supported by IE9 but in IE8– (and compatibility mode). When we set IE9 mode in IE9 Dev Tools (F12) and go to Tasks list and try to create a task, we’ll get an error: It is RTE_GetEditorIFrame from init.js: