When I go to https://www.frameforge.com in Safari, the address bar doesn't contain the little padlock icon indicating proper SSL. But if I go to the same URL in FireFox, Chrome, or Edge, they do have a lock indicating that all is well. How can I figure out why Safari is not happy with this site's certificates or whatever?
Missing SSL padlock icon in Safari address bar
Looking at the Console tab of Safari Web Inspector, looks like there's a warning for mixed content. Fixing this will likely show the padlock icon.