With a mozilla-central nightly dated 2011-05-26 or later: 1) If you're running on OS X 10.6 or above, right-click on the distro and choose "Get Info". Then choose "Open in 32-bit mode". (The QuickTime plugin doesn't work in 64-bit mode.) 2) Visit http://www.2xstream.co.uk/mediaexamples/quicktime/qthistream.html. 3) First make sure the plugin isn't clipped on the left or right. Then start resizing the browser window. Notice artifacts on the left and right sides of the window. In particular notice many overlapping copies of the vertical scroll bar. By trial and error, I found that this started happening with the following patch: Bug 562746. Update cairo to 1.10. author Jeff Muizelaar <jmuizelaar@mozilla.com> Thu Mar 10 14:52:15 2011 -0500 (at Thu Mar 10 14:52:15 2011 -0500) changeset 70161 acb4e51fa8a6 I don't know what it is about QuickTime videos that triggers this problem. It doesn't happen with Flash or Silverlight.

Actually this bug's regression range is more complicated than I first thought: The problem stops happening with the firefox-2010-05-27-03-mozilla-central build and starts happening again with the firefox-2011-05-28-03-mozilla-central build and subsequent builds. But this makes sense because the patches for bug 562746 were backed out on 2011-05-26, and then relanded on 2011-05-27.

Oops, this bug happens even with the QuickTime plugin disabled. So it's some kind of Graphics, bug, and not a plugins bug. I suppose it has to do with the fact that the object in which the QuickTime plugin is embedded moves around when you resize the page.

But even with the QuickTime plugin disabled, this bug only happens in 32-bit mode (not in 64-bit mode).

The subject line should be changed ... but I don't yet know what it should be changed to.

Resolving this as incomplete since I have no way to replicate this issue. Please reopen if it still reproduces.