Weird Firefox rowspan Problem

%"§§"$&$!!! Firefox

And the same thing in IE11 (<3 ???) and everything else...

This is what markup and styles (likely irrelevant) look like. Same as the other rowspan cells in the screenshots...

And all border-styles as computed by Firefox. Am I missing something here? The code is at [https://alpha.surayt.com/tr/Level%20A2/9.2].