Every available and applicable about: dialog can be viewed, even those activated by other extensions.

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.

Historical note: ViewAbout came about from a need to view about:crashes in Thunderbird, and it just expanded from there.

Firefox Add-on page: https://addons.mozilla.org/en-US/firefox/addon/9695/

Thunderbird Add-on page: https://addons.mozilla.org/en-US/thunderbird/addon/9695