Attempting to install Server Certificate on NetScaler VPX fails with the error: "Object doesn't support property or method 'endsWith"

Problem

You’re attempting to install a Server Certificate on a Citrix NetScaler VPX NS12.1 49.23.nc with the required .cer and .key files but receive the following error:

"Object doesn't support property or method 'endsWith"

Solution

These error had me stumped for a while as I kept thinking this was caused by corrupted files but I realized a bit later that it was browser related.  This error would be thrown when I use IE 11.447.14393.0:

… but not when I use Chrome 70.0.3538.77.