My photos were blurred and I found in F12 developer tool that they failed to load. After a little fiddling with my network they successfully loaded and became clear.
It's not just you. It's basically unreadable on Firefox on Android (and what's worse... the page prevent arbitrary zooming, unless you "request the Desktop page").
It's depressing how a supposedly well-designed platform like Medium still falls short of providing an usable mobile interface.