Q: Facebook & YouTube not loading in Safari

Facebook was misbehaving last night, but I assumed a reboot would fix it. Still the same this morning, and I see the same problem is affecting YouTube... basically Safari is only loading the most basic version of the page, with no CSS, dynamic content or graphics. Links don't work. Nothing works!

Other feature-rich sites (such as Twitter, Gmail, BBC iPlayer) work fine - I haven't been able to find the same problem elsewhere. Just FB and YT.

I haven't checked extensively, but this only seems to be a problem with Safari... however, it's affecting two different Macs, one with El Capitan, the other with Yosemite. It doesn't seem to be a wider OSX issue, as both sites load fine in Google Chrome on the same computers.

Here's a screenshot. This is Safari 9.0.3, OSX 10.11.3, Mac Pro 2009...