ScrapBee helped me "recover" most of my Scrapbook files. Unfortunately some of my saved pages are no longer online and I see a 404 error instead.

There are additional steps after installing the extension. Go to ScrapBee's Configure or Settings page, then go to Install. You have to install the backend executable before you can add the filepath(s) in the Configure page. Once you're done with the filepath(s) section, click Save. I did not have to restart Firefox, but YMMV.