Klaus, can you take a look?

We really shouldn't be giving different render target sizes based on whether you were in the VR browser -- I don't think this is intentional.

I'm strongly suspecting that this is due to the application misusing window.devicePixelRatio. The render buffer dimensions in WebVR are raw pixel counts, they aren't supposed to be scaled by a pixel ratio. They should be used as-is for sizing the render canvas. Other WebVR applications aren't affected by this scaling issue.

When starting in regular 2D Chrome, window.devicePixelRatio is 3.5. When starting in VR Browser, window.devicePixelRatio was 1.7 when I just tested. That's a 2x difference and could easily explain the quality difference.

It's an application bug, it's resizing based on window dimensions in a way that overrides the provided recommended render resolution.

For context, I could reproduce the issue for http://vr.digitour.co.nz/ as mentioned in the original bug report. Inspector shows that it's using a canvas size of 576x385 pixels on a Pixel 2 XL. For comparison, https://webvr.info/samples/03-vr-presentation.html works normally on the same browser version, and uses a canvas size of 2288x1133 on the same device.

With some logging added, you can see that it's calling this._renderer.setSize with the recommended size, then overriding that:

resize 2288 1133 false
setPixelRatio 2288 1133 false

resize 2288 1133 false
resizeCanvas 576 385 true

The override happens here:

            key: "frame",
            value: function(e) {
                var t = e || 0;
                0 === this._lastFrameTime && (this._lastFrameTime = t);
                var i = Math.min(t - this._lastFrameTime, 100);
                if (this._lastFrameTime = t,
                this._needsResize) {
                    var a = window.innerHeight
                      , r = this._parent.clientWidth;
                    this._parent.style.height = a + "px",
                    this.resize(r, a),
                    this._needsResize = !1

Here, this._parent.clientWidth is 576 and window.innerHeight is 385, leading to very pixelated rendering.