The top of my screen is normal: the tool bar starts "File, Edit... The body of the screen while running Firefox-and during typing of this message- is full of lite. The actual data: starting from the top of this page- "Firefox Help... Ask a new..." etc. starts 5 1/4 inches from the left of the page. It's as if Firefox were presenting a wider page with the presentation moved to the right. This pushes the last, normal, 5" of the presentation off the screen. The rite end of the bar which starts out: http://www.mozilla.com/en-US/firefox/fx/ is off the page, so the facilities at the rite end are lost. Any presentation, including Amazon.com and Youtube.com are similarly pushed off the rite side of the screen by 5". I have no access to the rite-most 5" of any internet presentation. The sliders that move the presentation up and down and left/ rite are off the screen. I have shrunk the display down so small, i can barely see the numbers: Control panel\ display \ settings \ 1920 by 1200. This gives the ILLUSION of centering the presentation, but still no sliders. At this setting, i can see the full width of Amazon. Youtube appears centered, with 4 1/4" on both left and rite, but no edge sliders. I dropped the 'setting' to 1440 x 900. Lost about 3" off the rite side of Amazon; barely on the rite edge of Youtube. None of my local programming has a problem: Excel, pictures, videos, Word, even Internet Explorer goes full page and centered. I un-installed Firefox and downloaded it fresh. It did NOT ask me to reboot my puter, so i didn't . I can supply pictures (screen shots) of the phenomenon on request.