I mentioned earlier these plugins but nobody replied:
https://addons.mozilla.org/en-US/firefox/addon/epub/
https://addons.mozilla.org/en-US/fir...e-web-offline/
https://addons.mozilla.org/en-US/fir...n/saveasebook/
That seems simpler than copy-paste even.
Do you not use Reader mode in Firefox? It's superb, I highly recommend it. It's almost always superior experience than the formatting of articles otherwise. It includes photos usually. Exporting that as epub is totally sensible.
I've now tested those plugins, and none are perfect, some work better than others for different cases, but it's something. I'd like to know if people have other recommendations.
Otherwise I find Calibre can convert documents too.