This does happen Windows7 Aero. This happens Windows7 Classic or AeroBasic Steps to reproduce: 0. Make sure Window Visual Style is Classic or AeroBasic. 1. Enable e10s 2. Move browser window to protrude from the desktop 3. Resize the window by dragging left border Actual Results: Browser window stops redraw Switching taskbar button will redraw window Expected Results: Should not stop

> 1. Enable e10s The problem also happens with non-e10s window.

[Tracking Requested - why for this release]:

Regression pushlog: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=2a61df4eaa2d&tochange=24ba8274ed60 In local build Last Good: 2a61df4eaa2d First Bad: 823227372483 Regressed by: 823227372483 Bas Schouten — Bug 1107297: Only recomposite the damaged rect with D3D11. r=jrmuizel This patch makes us behave similarly to when we're using the BasicCompositor, essentially we will clip all drawing to the final display to the area that was labeled as invalid. When DXGI 1.2 is available we will then also report the damaged area to the Present call so that can then be used to minimize the amount of bits that actually need to be blitted to the screen. Since we're no longer recompositing the whole screen this means we should also only clear the damaged area of the window.

This seems ro be fixed by Bug 1117925 in m-c

s/ro/to

Confirmed it fixed https://hg.mozilla.org/mozilla-central/rev/06b590bf59f4 Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0 ID:20150121141530