Q. I can't log in with new incognito window with "This webpage is not available ERR_ADDRESS_UNREACHABLE" error.
A. You need to allow Force.com LOGINS extension to run in secret mode. You can do this at chrome://extensions/.
Q. Where is my login credential data stored?
A. The data is stored in localStorage of your browser, which means your data is stored locally in your computer. By enabling Chrome Sync feature at option page, the localStorage will be remotely synced between browsers. Chrome Sync feature is only available for paid edition.
Q. Are my data safe in localStorage?
A. Your data including login password are stored in localStorage in text format by default, so it is not very secure at first hand. You can enable encryption feature at option page to encrypt login password in localStorage. Don't forget to export data for backup before turning on encryption feature.
Q. Can I login to different accounts with different windows, without mixing up the login sessions?
A. The login session is kept in browser cookie and is associated with domain. If domains are the same over different windows then the session on those windows will be overwritten by the latest login.