I have found a workaround for readability in VR, this change in adv-vfr.css:
ingame-ui#AdvVfrPanel #AdvVfrPanelWrap iframe {
border: none !important;
height: 33.3%;
width: 33.3%;
-webkit-transform: scale(3.0);
-webkit-transform-origin: 0 0;
}
Depending how big you do the window, you can be intersted in more scale. Also depending on the HMD.
height and width must be “100 / scale”%