The internet tells me that Firefox has a bug that causes it not to display solid colored table borders properly. I have had this sort of table in most of my Joomla sites and never had a problem until the Ashley site I'm currently building. You can see the issue at http://blissberry.com/nubian/index.php/19-senior-doe/9-gch-blissberry-catch-me-if-you-can-5-m and on many more pages by following the Prev/Next links in this category.
The tables display properly in Chrome and Edge. When I first added these articles they displayed OK in Firefox, then gradually a few had missing borders and now all do. I've looked at the table code and compared it to sites that display properly and can't find anything that makes a difference.
I'm hoping you have a fix. Thank you.