I got this from here: http://shallowsky.com/blog/tech/email/mutt-viewing-html-mail.html

Here is the simplified version:

With this tip you will be able to open the complete HTML message content in a browser using e.g. F10 in Mutt.

Akkana wrote a python script that will extract a message including its mime-attachements into a temporary folder and open it with Firefox.

Setup:

  • Download the viewhtmlmail script.
  • Save it to e.g.: ~/.local/bin
  • Make it executeable: chmod +x ~/.local/bin/viewhtmlmail
  • Put this into your .muttrc:

     # macro  index  <F10>  "<pipe-message>~/.local/bin/viewhtmlmail\n" "View HTML in browser"
     # macro  pager  <F10>  "<pipe-message>~/.local/bin/viewhtmlmail\n" "View HTML in browser"
    

Now restart mutt and enjoy reading HTML-Mail in your Firefox by pressing F10.