Some of my firefox config settings.

user.js:

user_pref("browser.chrome.toolbar_tips", false);
user_pref("browser.sessionstore.enabled", false);
user_pref("plugin.default_plugin_disabled", false);
user_pref("image.animation_mode", "once");

chrome/userChrome.css:

.tabbrowser-tabs .tab-text {
  font-size: 11px;
}

menubutton, menulist, menu, menuitem {
  font-size: 10px !important;
}

chrome/userContent.css:

input[type=text], input[type=submit], select {
  font-size: 10px !important;
}