recepies/firefox/userChrome.css

window {
  font-size: 12px !important;
}

menubar, menubutton, menulist, menu, menuitem, textbox, toolbar, tab,
tree, tooltip
{
    font-size: 11px !important;
}
1	window {
2	font-size: 12px !important;
3	}
4
5	menubar, menubutton, menulist, menu, menuitem, textbox, toolbar, tab,
6	tree, tooltip
7	{
8	font-size: 11px !important;
9	}