iMac i3, Firefox 60: Images not loading from Imgur

I'm running an iMac i3, and I've run into this weird issue where certain forums—not this one—won't load images linked from various hosting sites like Imgur... It's especially stupid because it won't even show photos from Imgur, even though I have my own account there and all my own uploads display perfectly fine—but when I try to view links to anyone else's photos or albums on that same service, it just fails.

Hmm. We're having trouble finding this page.

It is impossible to connect to the server at imgur.com.
If that address is correct, here are three other things you can try:

Try again later.
Check your network connection.
If you are connected but behind a firewall, check that Firefox Has permission to access The web.

Obviously, reloading isn't the fix here—my connection is fast and stable—and the firewall suggestion is useless; if a firewall were blocking Imgur, my own photos wouldn't show up either, yet they work fine for me, while everyone else's links just trigger that error message above...

I have the firewall enabled on my iMac (system is always updated, currently on macOS High Sierra 10.13.5, using Firefox 60).

Any idea what's causing this? (Everything else works fine—audio, video, images—on basically any site. This is a private home setup, not some corporate network with strict traffic controls or proxies...)

Is anyone else seeing this on a different browser?
Some of these image hosting sites just flat-out block direct linking from certain domains.
Got an example we can test out...

None of my browsers—whether it's Tor, Safari, Chrome, or Firefox—are loading anything right. They all have their own little quirks, but it always comes back to the same loop: either they can't find the host, I'm supposedly blocked by a firewall (which doesn't make sense since it happens whether that's on or off), or people are just guessing the host is too busy...

Logic says the error has to be in my system settings, but if that were true, why does everything else load perfectly? I can view any photo on the web—even my own albums on these same sites—without an issue. Yet, when I try to pull someone else's photos from those exact same services, it claims their host is "unavailable." It makes zero sense.

Whether you have a fire extinguisher handy or not—the result stays the same.

Alex Booth3 said:Logic suggests the issue should be in my system settings, but if that were true, why does everything else load fine? I can see all my own photos on various sites without a hitch, yet when I try to view someone else's stuff on those exact same services, it claims their host is "unavailable"...???

Whether you have a fire extinguisher handy or not, the house is still burning down.

And does another computer on that same network show them up normally?

It’s a home network—everyone else on their Windows laptops is happy, so clearly everything is working just fine...