GeometryInstance Doesn't work in IE (only in chrome)

The following code block will only work in chrome and not IE (edge):

    var _OL = new Cesium.GeometryInstance({
        geometry: new Cesium.PolygonGeometry({
            polygonHierarchy: {
                positions: Cesium.Cartesian3.fromDegreesArray([-95.28760453993358, 29.75117274029189, -95.29005754099585, 29.75238558348876, -95.29102201131342, 29.74915372223278, -95.29139019024684, 29.74918519321223, -95.29156626623544, 29.74888630608471, -95.29190585054992, 29.74877641283107, -95.29293642033977, 29.74808506462816, -95.29358386034178, 29.74768012176543, -95.29369379439542, 29.7467062372499, -95.29347262783625, 29.74670634867498, -95.29253545155771, 29.7261636024184])
        id: '_OL',
        attributes: { color: new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5) }

    __OL = new Cesium.GroundPrimitive({ geometryInstance: _OL });

In chrome, a light-blue overlay will be added to the viewer, in IE however nothing happens.

This is expected behavior, as mentioned in 1.13 CHANGES

Added support for GroundPrimitive which works much like Primitive but drapes geometry over terrain. Valid geometries that can be draped on terrain are CircleGeometry, CorridorGeometry, EllipseGeometry, PolygonGeometry, and RectangleGeometry. Because of the cutting edge nature of this feature in WebGL, it requires the EXT_frag_depth extension, which is currently only supported in Chrome, Firefox, and Edge. Apple support is expected in iOS 9 and MacOS Safari 9. Android support varies by hardware and IE11 will most likely never support it. You can use to verify support for your hardware. Finally, this feature is currently only supported in Primitives and not yet available via the Entity API.

So basically, IE doesn’t implement the extensions to WebGL needed to make this work, and since IE is superseded by Edge, I doubt it ever will.

Now I will agree that silent failure may not be the best way to handle this case, so we will eventually explore better ways to make developers aware of the incompatibility; but ultimately apps that use vector data on terrain are going to have to have different code paths if they want to work on all browsers. We may add an automatic fallback when we add these features to the Entity API, for example.