I find a lot of sites that use text color from fairly light to medium gray, on white or light gray background which doesn't show up well. Some have so little contrast, it's like they're ashamed of the content. The problem I expect from using a blanket statement in userContent.css, even if it mostly worked, is there will be some background colors that won't contrast well with black text; trading one problem for another. If I try to set all backgrounds one color & all body or paragraph text to another, there will be other elements on pages that won't show up. One example - in Preferences / Colors, when "Override the colors specified by the page with your selections above - Always" is checked, it makes addon's UIs totally unreadable. Clearly, that won't work for pages with elements besides text. Elements on some sites just disappear. I'm not sure what type of sites today would work using override all colors with black & white or where any 2 fixed colors would work on most sites. Is there a way to detect when sites use background / foreground colors with contrast below a certain value and only then change text to black? That would assume the background was a light color. If a dark background was detected, light text would be needed. It may be that sites have so many different types of elements / graphics, something like this would be impossible.