To develop and test features specifically for build 9600.16428 :
Use this tool to automatically add the -ms- prefixes required for IE11 layout support. internet-explorer-11-0-9600-16428-final-kuyhaa
IE11 does not support (Custom Properties) or CSS Grid (it uses an older, prefixed version). To develop and test features specifically for build 9600
Use the "Emulation" tab in IE11 to simulate different document modes, though testing on the actual hardware/OS where that specific build is installed is more reliable. internet-explorer-11-0-9600-16428-final-kuyhaa