これの事なら53じゃなくて56.3じゃね

There is now a complete backup of all classic add-ons from the Mozilla Add-On Store,
mirrored on the Waterfox CDN. You can use the Classic add-on Archive add-on to view
the catalogue. This will be integrated into the next minor Waterfox version (56.3).
https://blog.waterfoxproject.org/waterfox-56.2.5-release-download