Occasionally (on desktop and on Android) gray lines will appear in content when content scrolls. This is reproducible on Fennec with this page: http://people.mozilla.org/~bstover/invalidate.html (press S to step, or any other key to scroll automatically) Fennec also needs a patch that listens to scroll events from content, which will be attached shortly.

Note these are not actually gray lines, but actually lines where content is 'faded' as if a layer containing the content was blended to a white background, but not completely covering those pixel rows.

Without the patch, there are no lines but I see: ###!!! ASSERTION: Messed up quadants (ThebesLayerBuffer.cpp line 164) Also, I was wrong; Fennec already listens for scroll events. This patch just ensures that setDisplayPort isn't called when content scrolls. The problem may be easier to figure out with cjone's test browser XUL.

Reproducible on test-ipcbrowser.xul, with resolution and scale at 0.7.

Pushed http://hg.mozilla.org/mozilla-central/rev/05937e37d81d