Customize the boring menus in firefox as you like.Menu Editor is an extension that allows you to customize the menus in Firefox and Thunderbird.
Related:Seven Hidden Commands in Firefox
Firefox users just click the link below and install the extension.
Install Menu Editor version 1.2.4 for Firefox 2 and 3
To install Menu Editor in Thunderbird just right-click this link, choose "Save Link As" and install the downloaded menuedit.xpi file using Install button in Thunderbird’s Extensions window.