I've run into an odd text rendering issue with Firefox. I have a div that is rotated, and another div inside it has it's opacity rapidly changed between 1 and 0.5. This causes any text inside the div to render differently each time the opacity changes - some numbers will shift up or down by a pixel, parts of the text will be thicker or narrower.
As an example, this:
<div class="glowy transparent"></div>
<p class="someText">1 2 3 4 5 6 7 8 9</p>
transform is already there and
-moz-backface-visibility: hidden; useless you may use a filter to force FF render calculation, so you cure also the stair effect on edges.
filter: blur(0.1px);/* note that even 0 as value does it */