Hi Jacqueline,
Thanks for the credentials, this is weird because the issue is only happening in Firefox, not on Chrome. But when I imported your page and theme options settings on my dev site, I don’t see the issue either on Chrome nor Firefox.
So this issue seems to be beyond just the content. Would you mind doing a testing for a plugin conflict? You can do this by deactivating all third-party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
And also, please contact your hosting and ask if or how you can update the MYSQL version to 5.6 or higher.
Let us know how it goes,
Cheers!