I run Nightly as my daily driver and I don't have this addon installed.

Edit: Apparently some have: https://bugzilla.mozilla.org/show_bug.cgi?id=1424977#c0

Define "affected". The extension might have gotten installed. The extension did not actually do anything, though, if you did not enable its function via about:config.

Nightly was, so I assume any with experiments turned on.