This add-on scratches an itch.  It doesn't add new functionality, it
just streamlines.

Like in many applications these days, the 'Tools' menu is a misnomer:
it often contains essential and not just auxiliary functionality.
Thunderbird is particularly hopeless in this respect, as it not only
has the general 'Preferences' dialog hidden in this menu, but also the
separate 'Account settings' and 'Add-ons' dialogs.

Firstly the 'Preferences' dialog isn't a "tool" and should therefore
not appear in this menu. Secondly, other dialogs that modify the
application's settings should really be part of the general
'Preferences' dialog.  That way they will also be available under the
common shortcut for invoking the 'Preferences' dialog.

This Thunderbird extension fixes all this.  Well, for now at least the
latter.

Most of the code in this extension is taken from Mozilla projects and
(c) their contributors.  Thus this extension is released under the
same license, the Mozilla Public License Version 1.1.