On a Mac, when you type Option-Shift-R you get the sign for 0.1%, which is "‰ "

The "%" sign is Shift-5. Option-5 gives the leminscate, otherwise known as the sign for infinity: "∞"

It would make sense for Option-Shift-5 to be related to a number, but instead it's "ﬁ"

No, I did not just type "f" then type "i." Oddly enough, Option-Shift-6 gives you "ﬂ"

How in the world did the R-key get roped into percentages? Option-R is the registered trademark symbol (®), which makes sense since it contains, y'know, an R.

Yes, I understand the concept of typographical ligatures, but what makes ﬂ so special? We could have had a few more Greek letters instead.

Wherein unreasonably free time is dedicated to proving Jonah Hill is funnier than you.