For one reason or another, I reinstall an OS every couple of years or so, and start out with a fresh Firefox instance. I invariably end up with the same 14 or 15 extensions (delta is due to Linux work laptop vs Windows home PC). I use them all, but obviously my reliance on them follows the 80:20 rule.

I had them all synced for several years, surviving several data-losing crashes. I realized how I didn't actually use most of them.