Maybe you are using an adblocker that is too aggresive. Try changing your adblocker settings, or use a different adblocker - or turn your adblocker off, while you are using that site.
Do you have the same issue with any OTHER web sites?
Also, older versions of Safari (as well as older versions of other web browsers) might be blocked out by that site (Adorama.com) Your Firefox is (almost) current, where the Safari 11 is several years old. If you can't upgrade your macOS version to get a newer version of Safari - at least you do have the option of updating your Firefox to current version 71.
You might be able to find out more information by "contacting the site website administrator at
info@adorama.com". That site may have tightened restrictions for the holiday season. They may even tell you to "use a different browser, such as Firefox"