Changing the background color
Re: "In your firefox preferences, choose language and appearance, under font, check you have background set to white, and text set to black."
Any screenshots for this example? I use 8 different browsers and Firefox is the most counter-un-intuitive browser I've ever used. Why would Settings refer to "Language" to set the background color? There is no link that I can use to Fonts and Colors under Language and Appearance to change the background color. All I can do is select a Default font, Size, Advanced, and Colors. But In colors the Background is evidently set to white but it's actually black. So I must map my way around Text and Background, Text, Background, Use System colors, Override the colors specified by the page with your selection above, Only with High Contrast themes, Link Colors, Unvisited Links, Visited Links, Underline links.....yada yada yada blah blah blah.
But what do you want to achieve? To change a background color of what?