User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b6pre) Gecko/20100906 Firefox/4.0b6pre Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b6pre) Gecko/20100906 Firefox/4.0b6pre Just noticed this about two days ago when I updated to the latest Minefield build (this issue doesn't occur in Firefox 3.6.x). When you hover over one of the "inactive" images, Minefield shows a large black border around the image for a second or two, as well as when you move the cursor away. I remember seeing some box-shadow fixes filed in lately, perhaps it's due to that? Reproducible: Always Steps to Reproduce: 1. Hover over any of the inactive images in "Top Video Game Content". 2. Watch the border around the image. 3. Watch again as you move the cursor away. Actual Results: A black (semi-transparent?) border appears around the image briefly. Expected Results: There should be no border. Using the default theme.

I'd rather say it's because of the Combination of Hover Selectors and set Opacity. http://www.greywyvern.com/?post=317 is a good Example of how several CSS3 Rules (border-radius, box-shadow, transform:rotate, text-shadow) combined with that are affected by (defect) accelerated Layers rendering.

tooltips on tbpl are a great way to reproduce.

Fixed within: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=fa55e317302a&tochange=9aecc4392dad => Bug 596152