I found the issue to be caused by Facebook’s browser displaying text slighter bigger than other browsers. This caused text elements which were tight to the boundaries of the box to wrap more than in other browsers, causing the overlapping, poor spacing, etc.
I went through all pages and all elements, adjusting the text boxes, making some fonts smaller, moving them, etc. Eventually, I got the pages to display close enough to the “proper” layout. It took some time, and was a bit of a pain in the ass, but I guess thats website compatibility testing for ya