Last year, I tried several epub readers on a linux amd64 laptop. None was satisfying. All those that just wrapped chromium crashed with some epub files: that was the case for "Foliate", which was the inspiration for this "Alexandria" project. The Calibre reader was slow and unresponsive. Mupdf was fast and stable, but it lacked important features, like a table of contents. A Firefox plugin was okay, but its workflow was impractical.
I've since bought a e-ink device, so I don't read much on my laptop. When I do, I use Koreader. It's perfect for my Kobo device, and quite alright for a computer.
A couple of years back I tried Zathura, with the mupdf backend (if I remember correctly, this was the needed plugin for epub, so I also ditched the Poppler backend for PDF). I'm not a keyboard centric user, so couldn't get accustomed to it, but still think it works pretty well.
I've since bought a e-ink device, so I don't read much on my laptop. When I do, I use Koreader. It's perfect for my Kobo device, and quite alright for a computer.