Simple Markdown viewer
Custom sites can be added in the Violentmonkey userscript settings. For custom CSS, see https://greasyfork.org/en/scripts/480759-styles-for-markdown-viewer.
Chromium: Enable "Allow access to file URLs" in the Violentmonkey extension options at chrome://extensions.
Firefox: There is a bug in Firefox that prevents any Markdown viewer from working: https://bugzilla.mozilla.org/show_bug.cgi?id=1319262. Use .md.txt instead of .md as a workaround until the bug is fixed. UPD: This will be fixed in Firefox 128 (which will be released on July 9th)
TODO: Describe another Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1267027 / https://github.com/violentmonkey/violentmonkey/issues/173 (summary: the reason the script doesn't work on GitHub).
