We're working on using some custom CSS in a Script Editor in our SharePoint 2013 environment and we discovered that the box-shadow which we are using does not display in IE9.
In looking into this it appears the default Seattle master page for SP2013 is hard-coded to have a "X-UA-Compatible" of "IE=10" instead of "IE=edge".
We tested our site using Chrome and IE10 and it displayed our box-shadow properly. IE9 however does not display the box-shadow.
I've thought about creating a custom master page which sets the X-UA-Compatible to be IE=edge but I'm not sure if that would break other aspects of the SP2013 sites or if there is an easier way to do this.
Any guidance you can provide is greatly appreciated.