Created attachment 216115 [details]
An archive containing a small html file illustrating the problem as well as a screenshot comparing Firefox and
When a table is styled with `border-collapse: collapse` and its cells have a border defined with opacity (e.g. rgba(0, 0, 0, 0.1)), a single border color should be calculated and uniformly applied throughout the border of the table. That is, regions should not get darker on edges and corners between cells.
Gecko seems to do this much better than WebKit does, although it’s not perfect (see the slight diagonal at the corners). I’ve attached a sample document that illustrates the issue, as well as a screenshot that compares Firefox 24.0 and Safari 7.