You can have footnotes within page for ebooks that support adequate EPUB attributes, and you also can activate with some additional user style tweaks. More info can be found here.

Image with footnotes within page can be activated with Document → Style tweaks → Miscellaneous → In-page footnotes and it looks like this:

Image where you're setting additional style tweaks:

You can also have footnotes popup by selecting this setting Settings → Links → Show footnotes in popup and it looks like this (footnote in popup after tapping on footnote link):

Useful info can be that touch zone for footnotes can become larger, in case you have problems targeting your footnotes on your device. More info can be found here.