CSS diagonal border aliasing in Firefox

Question

I drew a shape by using the border properties in CSS. It looks fine in Chrome, but in Firefox the borders are really ugly:

.shape
{
 width: 100px;
 height: 50px;
 margin: 0 auto;
 background-color: #3F7296;
 position: relative;
 color: #FFF;
 line-height: 50px;
 font-size: 40px;
}
.b1, .b2
{
 position: absolute;
 left: 100px;
 bottom: 0px;
 width: 0px;
 height: 0px;
 border-style: solid;
 border-width: 0px 0px 50px 16px;
 border-color: transparent transparent transparent #3F7296;
}

.b2
{
 left: -16px;
 border-width: 50px 16px 0px 0px;
 border-color: transparent #3F7296 transparent transparent;
}

<div class="shape">
 <i class="b1"></i>
 <i class="b2"></i>
</div>

Fiddle: http://jsfiddle.net/Ly1dz111/

Screenshot from Chrome:

Screenshot from Firefox (Mac OS X)

How can I fix this in Firefox?

Answer 1

This is a known bug in Firefox's handling of diagonal borders, and the workaround is to set a scale transform on the element so that Firefox is forced to run it through an extra graphics step.

In your example, the solution is to set -moz-transform: scale(.9999) on the .b1 and .b2 elements. This forces antialiasing in Firefox.

.shape
{
 width: 100px;
 height: 50px;
 margin: 0 auto;
 background-color: #3F7296;
 position: relative;
 color: #FFF;
 line-height: 50px;
 font-size: 40px;
}
.b1, .b2
{
 position: absolute;
 left: 100px;
 bottom: 0px;
 width: 0px;
 height: 0px;
 border-style: solid;
 border-width: 0px 0px 50px 16px;
 border-color: transparent transparent transparent #3F7296;
 -moz-transform: scale(.9999)
}

.b2
{
 left: -16px;
 border-width: 50px 16px 0px 0px;
 border-color: transparent #3F7296 transparent transparent;
}

<div class="shape">
 <i class="b1"></i>
 <i class="b2"></i>
</div>