I found a problem with using the keyboard volume controls in full screen flash turning my screen white and freezing up Firefox. Here is how I fixed the problem.
I noticed there was no problem with using the controls when flash was being viewed in it's normal mode. I went into Desktop Effects, Advanced and took away the check for Suspend desktop effects for fullscreen windows and the problem is solved. Now the keyboard volume control does not turn the screen white when watching full screen flash. Hopefully this will help others that have experienced this issue.
I experienced the problem using an NVidea GT 220 graphics card. I do not know if this effects other graphics cards but if you are having the same issue this fix is worth trying.