pirc

To comment on the Pirc: statistically, Black fares much worse with the Pirc in relationship to the most successful counter to 1.e4, the Sicilian defense (1...c5).

You could place a Java applet on your website which connects to an IRC server, such as pirc.

The Pirc spike in the 1850s looks interesting visually, but keep in mind that your data set back then is incredibly small.

As white - open sicilian, winawer french, advance caro kann, be3/qd2/f3/o-o-o stuff against modern/pirc, bd3 bd2 o-o-o against scandi.

So, e.g., Pirc Musar and her husband Aleš Musar have identical surnames.

Learn the pirc defense for when you play black.

From a gameplay perspective, Black has to commit much earlier with the Pirc than the Sicilian, since the Sicilian has about a billion variations starting as early as the second move.

Did people stop playing the Pirc due to sub-par results compared to other openings at the time (like I imagine happened with the Vienna) or did it simply fall out of fashion?

Nf3 openings as white, and King’s Indian Defense and various Pirc / French / Caro-Kann lines that allow either player to pretty much veer out of theory-heavy variations and reach early positions in which there are no sharp tactical edges to the game and your opponent could not generally have forced any without entering a dramatically losing position.