DMN table header border partially missing in Firefox

Problem:

• open cockpit dmn table in FF
• make sure details are hidden
• border between table head and table body is partially missing (see screenshot)

Reason:

• FF has problem with the rowspan="4" of the annotation and hit-policy cells when there are only two rows

Solutions:
1) Use the table body to render the border
2) Update the rowspan when details are hidden

Possibly related problem:

• If the table contains no rules, no border is rendered in Firefox (see other screenshot)