Can't Connect to Wikipedia

I figure I'll just spell out what exactly I did:

1. Today I went to Wikipedia for the first time since upgrading to Sierra. (so that's likely a factor) At first, I was able to view articles, but no images would load. Several minutes later, any wikipedia page resulted in a message in Safari to the effect of "can't establish a secure connection to https://wikipedia.org/"

2. I did a quick search but found no similar topics from support forums in 2016, all were for older versions of Safari. (I have 10.0)

3. I attempted to connect to wikipedia via Chrome and Firefox. Chrome produced the same result, no secure connection, no web site. Firefox mysteriously works just fine.

I'm not a network specialist by any means, but I'm familiar enough with basic encryption to know I haven't inadvertently turned on extra security, changed any settings or altered my network in any way that would block the site. Since Firefox can load it, it would seem it's not being blocked by the OS/firewall. I did see there's a support article saying that Safari 10 won't connect to "non-secure sites" but frankly I connect to less-than-ideally-secure web sites on a daily basis for my job, using the same computer.

Any thoughts? Maybe I'm not aware of new security settings in Sierra that would resolve this?