A Thunderbird bug 369482 occurs in Xfce 4.4.2 but not always Gnome or Fluxbox.
Could somebody at least verify this bug (for Thunderbird site) occurs using Xfce?
The password window is transient to the main Thunderbird window, so it's placed on the same default as the Thunderbird window.
both Metacity and kwin behaves the same in that case (tested with metacity 2.22.0 and kwin 3.0 on 4.1.2 on Fedora 9). No bug in the WM here, it's Thunderbird that sets its transient property wrong.