Is it possible to tell Firefox the printable fields, as well as what might or should be in the header or footer? I would like for me to be able to leave page numbers in the footer, but not delete the URL and header above. I was wondering if there is a CSS option or something that I would indicate on the webpage I'm working on.
Unfortunately, the latest version of Firefox (7) and, possibly, some earlier versions do not allow to adjust the fields, at least not in the version of Ubuntu / Linux.
For the size of the field, you can use the @page rule.
@page
From http://www.w3.org/TR/CSS21/page.html#page-margins :
@page { margin: 3cm; }
Avoid px , em and percent, and use mm , cm , pt or in .
px
em
mm
cm
pt
in
I do not know how to change what prints in the header and footer except the browser.
Yes - File → Page Setup → Fields and Header, then enter 0.25 for each (etc.)