IIRC you can use the browser to view them, i.e. a keystroke opens it in the brow...

_pfxa on Jan 16, 2018 | parent | context | favorite | on: Thunderbird Starts Working on Improving Its Interf...

IIRC you can use the browser to view them, i.e. a keystroke opens it in the browser. In Gnus I hit "K H" for that. Emacs also has SHR, a renderer for HTML, but it doesn't do all that good with complex documents.