Getting non-Aero toolbars for Thunderbird 5 on Windows 7

Thunderbird 5 brings a custom chrome on Windows Vista/7 that uses translucent Aero decorations on toolbars and menubars. Here is how to restore solid backgrounds if you don't like it.

Put the following into chrome\userChrome.css in your Thunderbird profile directory:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
window {
  background-color: -moz-dialog !important;
}

(Re-)start Thunderbird afterwards.

If you need more info on where the userChrome.css is supposed to be, cheat with the note on how to remove buttons in the message area.