View HTML Mail in Browser

[Felix Natter <fnatter@gmx.net>]

hello Gnus users,

I would like to view complex HTML mails in Firefox.

I found this (https://www.emacswiki.org/emacs/MimeTypesWithGnus):

(defun my-gnus-summary-view-html-alternative-in-firefox ()
  "Display the HTML part of the current multipart/alternative MIME message
    in mozilla."
  (interactive)
  (save-current-buffer
    (gnus-summary-show-article)
    (set-buffer gnus-article-buffer)
    (let ((file (make-temp-file "html-message-" nil ".html"))
          ;;(handle (nth 3 (assq 1 gnus-article-mime-handle-alist))))
          (handle (caddr (assq 1 gnus-article-mime-handle-alist))))
      (mm-save-part-to-file handle file)
      (browse-url-firefox-new-tab (concat "file://" file)))))

Note that I changed the (nth 3 to (caddr as mentioned on that wiki page.

Sometimes it generates the .html but does not open the browser, but
often it just shows the headers of the selected article, and does
nothing (at least in *Messages*).

I am using Gnus v5.13 with Emacs 26.3.

Is there a modern best practice for reading non-trivial HTML mails?  I
know about shr, but it often fails.

Thanks and Best Regards,
Felix
--
Felix Natter