Steps to Reproduce: 1. Open these URLs in tabs: http://www.google.com/ http://www.mozilla.org/projects/minefield/ [anything else] 2. Use Ctrl-Tab to bring up the new Tab-Switcher 3. Examine the previews for google and the minefield startup page. ACTUAL RESULTS: Some images in the previews have borders added around them. These aren't just JPEG artifacts, AFAICT. EXPECTED RESULTS: No new borders should be added in the previews. See screenshots for examples. (I've added red arrows to point to the borders.) I'm testing using a fresh mozilla-central debug build from today.

This screenshot shows that the added borders aren't always the same. In this case, a top border was added around the Q-shaped QMO logo on the left. (This top border was not present in screenshot 1.)

My guess is that what's happening is that the image is RGB24, with a solid white background.. but we're hitting the EXTEND_PAD failure here, so we're sampling outside of the image bounds and getting solid black (because we're doing RGB24) compositing. This is kinda broken in a lot of ways, but I really don't know what the right fix should be.

Yep. This might be fixed by roc's work in bug 458487.

(In reply to comment #3) > Yep. This might be fixed by roc's work in bug 458487. I'm still seeing the borders around the QMO logos (attachment 333272 [details]).

Currently we're not pixel-snapping when there's a scale in the context, so these fringes are sure to happen.