I have a MacBook Air, I think 2011 or some such. Just upgraded to Mac OS High Sierra, and I have Safari 11 on it. Suddenly Safari is not rendering pages properly. To illustrate: Laptop Monitor. Shows correctly. Now external monitor: See the whitespace? When the page first renders it actually shows that content, and if I click on those whitespaces it actually clicks through the content underneath. So I know it is actually downloaded to the client. Also if I take this page and drag it to the laptop monitor, it shows correctly. It only does this on Safari (not Chrome), and only on the external monitor. It's not unique to My Yahoo, I've seen this or something like it on other sites. In fact HTL also demonstrated one flavor of it. For example when I was figuring out how to show these images in this thread, I tried the "image" button in the Rich Text Editor, which displays a pop-up accepting an image URL. That pop-up does not render properly on Safari, on external monitors. I'm using a DisplayLink box to connect the external monitors, so yes I'm aware that could be a part of the puzzle. But it wasn't until I upgraded to Mac OS High Sierra. I just wonder if anyone else has seen this or has ideas.