I wonder if anyone can help me with this. I understand the concept of UA stylesheets. But I'm confused about the difference between a UA stylesheet and browser options/preferences. To clarify - I know I can change the font face, size and colour in Firefox but those changes do not appear in Firefox's default stylesheet. If I check my changes in Firebug, the element changes are shown in the computed tag. So, for example, if I change the font size to 20px and the colour to Maroon, and then click the <p> element in Firebug then click computed, those changes are shown. But when I open the Firefox stylesheet, they are not shown.

I may be a bit gormless on this but would welcome any help and clarification.