The same problem with the plugin on KDE. In spite of the [MIME solution by Firefox user 15126385](https://addons.mozilla.org/en-US/firefox/addon/markdown-viewer-chrome/reviews/1453572/) works perfectly, I have to refresh the page or change any of settings to see the content instead of blank page.

Plugin v. 3.8
Firefox v. 74.0

P.S. That solution for KDE should have appearance in the Documentation.