The feature will enable you to easily and quickly grab the contents of your GMail inbox using RSS feed. To try that feature, just use this URL as your RSS feed URL:

https://USERNAME : PASSWORD @ gmail.google.com/gmail/feed/atom

Replace the USERNAME with your GMail username, and the PASSWORD with your GMail password. You need to paste that URL into your browser address bar and you can start to read your email. That is so easy.

Otherwise, I think this is not a good idea to have your password shown on the browser. Especially, if you are using public feed aggregator service, like feedburner, since they might get your GMail password.