Really slow initial loading of site

For the last couple of days, every time I visit the site, it takes a really long time to load, almost to the point that I think it's going to time out, then it finally loads and everything is fine, with no slowness.

This started happening yesterday at work (we have a 1Gb connection). Every other site loads normally, but TSF takes 30 to 50 seconds before finally loading in my browser.

It's also happening at home (60Mb connection) and on different computers, but all other sites load at normal speeds.

I use Firefox, but it happened with Chrome, too.

 

Now it seems to be loading quickly in Edge, but still slow in Firefox, so maybe a Firefox thing? It's happening in Firefox on multiple computers, so that seems to be the most likely culprit for whatever reason.

 

As of today, it's back to loading normally.