To rule out a settings/add-on issue, could you try: '''New Profile Test''' This takes about 3 minutes, plus the time to test your site. Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. Click the "Create a New Profile" button, then click Next. Assign a name like May2019, ignore the option to relocate the profile folder, and click the Finish button. After creating the profile, scroll down to it and click the '''Launch profile in new browser''' button. Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test. ''Any difference when you check your site in the new profile?'' When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile.