There is a fundamental disagreement between Chrome Legacy and Firefox on caption size influence on table width. Chrome uses caption min width as lower limit of table's grid box, FF does not. Firefox also does not support multiple captions.
Caption width limits
Caption minmax and grid width
caption.min is lower limit of grid min.
Caption.min vs caption.css_width
Caption.css_width is upper limit of caption.min
Caption.css_width is lower limit of caption.min
Caption width:50%
Percent width is resolved wrt to table width.
Caption and size of empty table
  Larger of table borders, and caption min size.
Caption height:80%
github spec issue.
TablesNG will not resolve percentage heights per spec. FF agrees.
Multiple captions
Do we allow multiple captions? There are 4 in this test.
  over1
  over2
  under1
  under2
  | 2 above me, 2 below me? | 
Caption margins
Margins between captions do not collapse
  20px margins
  20px margins
  | 2 captions | 
Caption margins auto
auto margins center captions that are less wide than the table.
Vertical writing mode caption
  vertical
 caption bigger than table
  
    vertical! |