Reproducible on Mac 10.8 Retina and Windows 7 on Firefox 21.0 release and Aurora 2013-06-05. Does not reproduce when using -webkit-transform on Chrome or basic transform using IE10. Method: 1. Open attached file (transform.html). This file create two divs, applies -webkit-transforms to one of them, and animates the transformation using a step function. Result: The moving div animates over the static div. Expected: The moving div should animate under the static div, as it is drawn first in the DOM.

Update: > This file create two divs, applies -moz-transforms to one of them, and > animates the transformation using a step function. Mistyped -webkit-transforms in the file description. Should be -moz-transform.

Regression window(m-c) Good: http://hg.mozilla.org/mozilla-central/rev/4cb8f88213f5 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/18.0 Firefox/18.0 ID:20121003235718 Bad: http://hg.mozilla.org/mozilla-central/rev/0d90d5f3da5a Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/18.0 Firefox/18.0 ID:20121004082018 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=4cb8f88213f5&tochange=0d90d5f3da5a Regression window(m-i) Good: http://hg.mozilla.org/integration/mozilla-inbound/rev/a2da97e3ebc6 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/18.0 Firefox/18.0 ID:20121003210717 Bad: http://hg.mozilla.org/integration/mozilla-inbound/rev/1cceedd227a7 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/18.0 Firefox/18.0 ID:20121003211916 Pushlog: http://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=a2da97e3ebc6&tochange=1cceedd227a7 Regressed by: Bug 790505

Tracking is only used for recent critical release-specific issues.

Fixes the test case, I think this is probably what we want to do.

Comment on attachment 823696 [details] [diff] [review] Make animated transforms force all above content to be in a separate ThebesLayer Review of attachment 823696 [details] [diff] [review]: ----------------------------------------------------------------- ::: layout/base/FrameLayerBuilder.cpp @@ +506,5 @@ > + */ > + nsIntRegion mDrawAboveRegion; > + /** > + * True if mDrawAboveRegion should be treated as infinite, > + * and all display items should be considerd 'above' this layer. mVisibleAboveRegion is treated as infinite too, right? Fix comment. @@ +2218,5 @@ > + // Prerendered transform items can be updated without layer building > + // (async animations or an empty transaction), so we treat all other > + // content as being above this so that the transformed layer can correctly > + // move behind other content. > + if (item->GetType() == nsDisplayItem::TYPE_TRANSFORM && Use itemType