Since upgrading to FF4 the right-click menu has rendered poorly, missing the background color/image. It looks like the background flashes then goes away when the right-click is first done. I am using version Firefox 4.0 Beta 8, 1.7 of ElasticFox on Ubuntu 10.10. See attached screen-shot.
I can confirm this happens in Windows XP SP3 + Firefox 4.0 too.
Here is a posible fix:
http://dirty-code.blogspot.com/2011/03/problems-with-elastic-fox-in-ff4.html
That does make the popup readable again, but doesn't follow the theme the OS anymore. So not a fix but a good workaround. Thank you!