Whatever it is that serves up user avatars has been randomly(?) failing for the past several days. I've checked this on several different browsers. If you go to the "Users" page of any SE site, you'll find that at least half of the avatars are missing. This applies to both user-supplied images as well as the system-generated geometric icons.
I had this error too, but I found a solution. I only wish I knew why it was happening in the first place.
I followed the steps here, which means using Google Public DNS.
Here are the steps I followed, with the screenshots.
Right click:
Clicked on the current connection (should be WiFi or LAN), then clicked properties:
Select IPv4, then click Properties:
Type in new DNS addresses, 8.8.8.8 and 8.8.4.4 are both Google's:
www.gravatar.com’s server DNS address could not be found. DNS_PROBE_FINISHED_NXDOMAIN
if I open one in another tab. And I am getting this on two separate computers. My own pic is affected... – Laurel Jun 6 '16 at 16:11