Unfortunately do to limitations in the the provided APIs in Firefox 57, Session Manager cannot be implemented as a WebExtension add-on and will not work in Firefox 57 or higher. My only recommendation is to either not update to Firefox 57, use the Firefox ESR build or use a forked version of Firefox that does not remove support for add-ons such as CyberFox or Waterfox. Session Manager saves and re
![Session Manager – Get this Extension for 🦊 Firefox (ja)](https://cdn-ak-scissors.b.st-hatena.com/image/square/e35b08f219e2ff6697109f3e88b0b9255ca478f0/height=288;version=1;width=512/https%3A%2F%2Faddons.cdn.mozilla.net%2Fuser-media%2Fpreviews%2Ffull%2F61%2F61138.png%3Fmodified%3D1530208052)