I also use a Mac with Safari (Apple's own browser) and it doesn't see there's a problem, although I'm still running High Sierra OSX, as my Mac won't run a newer OSX due to hardware limitations. I don't know if that has a bearing or not. Mac OSX does tend to be more "awkward" for hackers etc. to get at/into, so this may explain it.
However, both Firefox and Chrome (I use them also) both state the site is insecure, as described.