[Users] External browser for HTML

[Robert Harkins]

Rendering of HTML emails seams to depend on the plugin being used and
the contents of the email.  Claws Mail has been compiled from git
repository on FreeBSD 12.1 (VirtualBox guest). Dillo and litehtml are
the plugins available.

Have I missed how to use an external browser to view an email?
Thinking of an action to save a temp file and open in browser.

Guidance and contributing to my education is appreciated.
Robert