If the built-in screens are unreadable, you may need to modify an external settings file...

First, exit out of Firefox completely.

Type or paste the following in the Windows 7 Start menu search box and press Enter:

%APPDATA%\Mozilla\Firefox\Profiles

In that folder, you usually will find a single semi-randomly-named folder. If you find more than one, try to identify the most recently updated folder.

Inside that folder, you should find the prefs.js file (or if Windows is hiding the .js file extension, a file named prefs of type JScript). This contains many, many preferences, so ideally you would just remove the unwanted one.

To edit prefs.js, right-click it and choose Edit. Do not choose Open, as Windows will then try to execute the script.

Can you find this:

user_pref("browser.display.document_color_use", 1);

If Yes, change the 1 to a 2 and then save.

If No, you might be using a Windows "High Contrast" theme. Paste this whole line at the end of the file and save it:

user_pref("browser.display.document_color_use", 2);

At your next startup, Firefox should use only colors specified by web pages and not override them.

For some reason the color changes seem to be stuck on this computer, as I have even uninstalled the Mozilla program and then installed another version but the screen still has a lot of black space that wasn't there before. Do you have any additional suggestions? Is there a telephone support line that I can call for assistance? Thank you.

Hi turek, were you able to edit the prefs.js file?

It's possible that Firefox has become incompatible with your graphics card/chipset drivers. This sometimes happens when the driver software changes, or when Firefox turns on new features.

Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement? If so, you can disable hardware acceleration in Firefox here:

"3-bar" menu button (or Tools menu) > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

Hello jscher2000, when I tried to edit that file it wouldn't let me save it. I have also tried to open it in Safe Mode twice but the majority of the screen remains black so it's impossible to see anything. However, when I go into the Internet via Internet Explorer everything looks like it should... so this problem is definitely related to Mozilla. When I hit the "3 bar" menu and then "options" the screen is almost completely black so I can't see the "Advanced" button - but several small white icons are visible but don't seem to do anything. Is it possible to speak with someone at your company by telephone to walk through this issue? Thank you again for the assistance.

Mozilla does not have telephone support. Also, it's a national holiday here.

If this occurred after changing a setting and you can't edit or rename the prefs.js file to disable those particular settings, you might need to use the Refresh feature. This article describes what that does: Refresh Firefox - reset add-ons and settings.