If you’ve re-bootstrapped with juju-core and are running the GUI locally by modifying app/config-debug.js with the requisite details, note that you may need to delete the certificates from the bootstrap node in Firefox. To do so, go to Edit -> Preferences -> Advanced -> Encryption and click View Certificates. In the Servers tab, scroll down to juju and click the ‘*’ entry, then Delete. After restarting the browser, you can go to https:// [bootstrapAddress] :17070 and re-accept the certificate.