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Why suddenly does my Firefox window only use the top 3/4 of the page with a blank dark box and a blank light box in the bottom 1/4 of the page?boxk

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I'm using Firefox 30.0 on a desktop PC with Windows XP. When I opened Firefox tonight, a box popped up for about 3 seconds which appeared to say "installing update". Then, when the Firefox window opened, the "normal" page only took up the top 3/4 of the window, with the bottom 1/4 of the window taken up by a blank dark gray square box on the left side and a blank light beige rectangle box on the right side. As I open new tabs, go to various web sites, etc., the boxes remain in the bottom 1/4 of the window, and there's a scroll bar on the right side of the window so can scroll to the parts of the page that are "under" the boxes. I'll send screen prints of this if there's someplace to send them.

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Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings, disables most add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

  • In Firefox 29.0 and above, click the menu button New Fx Menu, click Help Help-29 and select Restart with Add-ons Disabled.
  • In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

  • On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
  • On Mac: Hold the option key while starting Firefox.
  • On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
    (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".
Safe Mode Fx 15 - Win

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.