Why have some websites started encoding "ff" as a single character "ff"?

For example in Aeon:

what leads us to consider another person as no longer the same. One might think that a different set of rules applies to assessments of one’s own continuity – perhaps episodic memory is paramount from this perspective

What's the motivation? And why have I started seeing this only now? I expect some tooling somewhere has changed?

PS what is this "ff" charaer called?