http://bugs.winehq.org/show_bug.cgi?id=30966
--- Comment #3 from Jordan jordan@jordanhenderson.com 2012-06-20 20:03:29 CDT --- I can reproduce the problem doing the following, with w version set to 2008:
in a firefox 13.0 with 1 tab, open www.winehq.com open in a second tab open something like wine->about
open a new firefox window so that you have 2 windows. in this second on, URL = yahoo.com
for a short period, there will be black sections in one of the 2 firefox windows. the window updates from yahoo will correct them and potentially introduce them as well.