Borders not shown in Firefox with border-collapse on table, position: relative on tbody, or background-color on cell

Answer 1

Adding another solution for this (old) issue: This happened to me today, because I have a somewhat complicated table with multiple tbody. The only issue was actually that I had an opened tbody tag that was not closed. I deleted that tag and the borders re-appeared, without needing to change anything in my CSS. To clarify, my structure was something like:

  

    
Col1
Col2
  
  

  

    
Val1
Val2
    
Val3
Val4