User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0 Build ID: 20120312181643 Steps to reproduce: Placed resized images with opacity 0.5 above each other. Css changes hover state to opacity 1. Actual results: On hover images increase in size by at least 1px. Expected results: Should have stayed the same size. Seems to be related to aliasing. Hover over the images here - http://bobtipping.com/fftest/low.html - and see how the picture changes in size and the aliasing on the doughnut shape changes. P.S. seems dependent on screen resolution. Mine is 1920 x 1080.

I have added a commented out line in the css - /*img{box-shadow: #000 0 0 0}*/ - When active this fixes the bug by keeping the rendering the same.

zorotipping, according to your comment https://bugzilla.mozilla.org/show_bug.cgi?id=745549#c7 could you close your bug as duplicate of Bug 745549, because we have more info in this bug report. Thanks.