[afranchuk]

I've never personally used it for epub, but apparently mupdf works with epub files. It's my go-to PDF viewer at least. Just be sure to read the man pages as most operations are keyboard hotkeys.

[michaelmrose]

Mupdf is a better backend for zathura than it is a reader in its own right. It's UI is lacking most notably lacking the ability to access the index.

[maskros]

Make sure you use mupdf-gl rather than mupdf-x11; then press 'o' for toggling the outline/index/table of contents.

[michaelmrose]

Thank you.