In some cases we can fall into image tiling code when drawing backgrounds when we could have avoided this by being smarter about the fact that parts of the background may be obscured by solid borders.
background: transparent url("checker.png");
-webkit-background-size: 100% 100%;
border: 20px solid rgba(1, 1, 1, 0.5);
where checker.png is a 576x576 image.
*** Bug 78162 has been marked as a duplicate of this bug. ***