hello johnajones, please go through the steps covered in Websites look wrong or appear differently than they should - they contain the most common solutions for the issue you've described...

I've gone through all those steps except creating a new profile and fiddling with individual sites. Now trying the suggestions about zoom settings. Do they refer to Zoom Text program from AISquared? It seems that ZoomText and latest Firefox are a toxic combination. Are you familiar with that?

Make sure that you haven't enabled a High Contrast theme in the Windows/Mac Accessibility settings.

• http://windows.microsoft.com/en-us/windows7/turn-on-high-contrast

Make sure that you allow pages to choose their own colors.

• Tools > Options > Content : Fonts & Colors > Colors : [X] "Allow pages to choose their own colors, instead of my selections above"

Note that these settings affect background images.

See also:

• http://kb.mozillazine.org/Website_colors_are_wrong