Forked from Gmail Manager NG by Erik Nedwidek, based on Gmail Manager by Todd Long.
This fork is intended to be a supported version of Gmail Manager since Erik and Todd appear to have gone MIA.
Inside "Privacy" > "History" settings from Firefox Options page:
- you should have "Always use private browsing mode" unchecked and "Accept cookies from sites" checked
Since Firefox 45, if you use Privacy Badger add-on, you may be unable to log in to your accounts:
- in the Privacy Badger settings, allow cookies for accounts.google.com.