Hello Toni and thanks for your review :)

It's a known issue and there’s an open bug in the Firefox bug tracker to fix this limitation: https://bugzilla.mozilla.org/show_bug.cgi?id=1266960
Hopefully it will soon be fixed.

I've documented this limitation in the project README on GitHub: https://github.com/asciidoctor/asciidoctor-browser-extension#firefox

Cheers,
Guillaume