The best.

(edited March 2022) The recent update is great. Being able to automatically archive all the pages I visit gives me a lot of peace of mind.

Works perfectly, I never found a problem with it and it helped me uncover some deleted pdf files.

Have been using this since it was a Firefox Test Pilot project called "No More 404s". Never had any problems with it. It's one of those features that should be built into Firefox.