User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0a1) Gecko/20120210 Firefox/13.0a1 Build ID: 20120210031150 Steps to reproduce: Opening the attached file makes the whole browser lag for me, and resizing the window once opened is very slow. The page has a tiled radial gradient as body background. The performance on Opera and Google Chrome is excellent on my system. I found the issue while looking through some old experiments of mine. It was reasonably snappy back when I first created the page (May 2011) and that makes me think it is a regression. Additionally, the original page had four layered radial gradient backgrounds, which only would have made it worse. I tested in Firefox 10 and Nightly (13)

Last good nightly: 2010-08-17 First bad nightly: 2010-08-18 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=116f2046b9ef&tochan ge=9ef027bf2120 Could be "42545f8d4b10 Bas Schouten — Enable D2D by default again." and it works faster in the Firefox safemode (HWA disabled)