Created attachment 56868 [details]
When I request a border around a box like this:
<div style="border:40px solid rgba(0,128,0,.5)">X</div>
then the semi-transparent border is drawn twice over each corner of the box. In other words, the vertical and horizontal parts of the border overlap in the corner.
Tested with WebKit-r60027. There are some similar bugs, e.g. #21835, but they all seem to involve border radius or similar advanced border CSS, so I created a new bug instead.
FWIW, I'm seeing this in 533.19.4
*** This bug has been marked as a duplicate of bug 21835 ***
*** Bug 60364 has been marked as a duplicate of this bug. ***