Difference in HTML renderers

Depending on the browser (and its corresponding render engine), I get two different render results.
I get the expected rendering when I use Firefox (Gecko) or Edge (EdgeHTML), but I get a much lighter version with Opera (Blink).
Chrome (Blink) seems to jump between both versions as I resize the windows.

Have you seen this type of behaviour before?
Is there anyway to counteract this? I’ve tried messing around with the CSS/JavaScript generated by Unreal Engine 4.13 with no joy.
I have all the default settings, material quality turned to low and plugins disabled.

P.S. I’ve posted two related Q’s on Answer Hub here and here