In a 2 monitor set-up, when I disable the primary monitor, and enable the secondary or vice versa, firefox4 will turn black upon changing the page (scrolling, viewing a different tab). http://i56.tinypic.com/r2lstw.jpg It does not turn black on: -enabling a second monitor -moving the window to the second monitor if the primary monitor is still enabled. Switching the monitors back or re-enabling the primary monitor will return firefox4 to normal. In order to switch to secondary monitor only, firefox4 needs to be forcibly closed and reopened. It can be closed normally while black, but I have to guess where the close button is. http://i56.tinypic.com/21ep88y.jpg