Seen on Windows 7, might happen on other Windows operating systems as well. When resizing the window either by using the edge or corner of the window, there is a large lag in rendering the content of the firefox windows [chrome + tab contents]. This is a very visible lag as the window just colors the new additional space white. This greatly affects the users perception of Firefox's responsiveness especially when the user is just playing around with the edges resizing and seeing the content refill.
Happens here too. Intel HD3000.
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