Safari blocking an important website
Why can't I access glwd.org (a great nonprofit organization) with Safari using my Macair?
MacBook Air
Question marked as
Yosemite, does not have a current version of Safari. Apple stopped supporting Yosemite when High Sierra came out a couple years ago. You can try Firefox for Yosemite if you are running that. You can also upgrade to El Capitan which any Yosemite machine can run. https://discussions.apple.com/docs/DOC-8811
explains how to upgrade. Note: Safari on an iPad opens the website fine. So it probably is the age of the certificate on your older browser.