Problem solved. Firefox thought I had two monitors. Right click on program in taskbar, choose move, then hold down left arrow key to bring the window back to the "right" monitor.

FF 4.0 simply refuses to open or opens without displaying page -- I get a fleeting glimpse of the browser page but it zooms off the screen on the right. When I right click the Mozilla program symbol on toolbar at bottom of screen and click "minimize" I again see the browzer screen very briefly when it zooms back from the right of the desktop. I uninstalled 4.0 and went back to 3.6 but it still does it.