the ligature is obviously there in my copy of the font.
You are aware that `Aufführung' *without* an `ff' ligature is the
correct way to write this word in German? `Auf' is a prefix, and as
such it should not have a ligature with the rest of the word. A
famous example of a similar situation is the word `Dorfladen' (a small
shop in a village), where an `fl' ligature gives very strange
connotations (Fladen = cow dung). Ditto for the word `Auflage': With
a ligature, it looks like a French word...
In other words, you should insert a U+200C `ZWNJ' (zero width
no-joiner) character between the two `f' characters.