ViewAbout is a Firefox, Thunderbird, SeaMonkey and Sunbird extension that allows every available and applicable about: dialog to be viewed, even those activated by other extensions.
about:, about:buildconfig, about:cache (and related), about:config, about:crashes, about:credits, about:license (generic Toolkit license), about:mozilla, about:neterror (seemingly useless), about:plugins, about:privatebrowsing, about:rights, about:robots, about:sessionrestore, about:weave.
These windows can be closed using Ctrl (or Cmd)-w. Note that some about: menu options may not show up in applications that do not support them.
Code now resides at Google Code: http://code.google.com/p/viewabout/
· Mozilla Sunbird