Firefox 58 Quantum resulted in our old extensions not working anymore. But if you want to enable extensions and keep using them, here’s what you need to do:

  • Download and install Firefox Nightly from here.

  • Start Firefox
  • Type about:config in address bar
  • and set the preference ‘extensions.legacy.enabled‘ to true
  • Restart Firefox.

You should now be able to enable multi-process capable extensions: