Installing Greasemonkey Scripts
Google Account Chooser Cleaner
One account. All of Google.
We've remembered your account on this device to make your future sign-ins easier. Just enter your password to sign back in.This is the new Google way, locking your account to a device and making it impractical to log onto multiple accounts on the same machine. Flushing the browser cache, history, and cookies doesn't clear it. Besides making gmail accounts difficult to use. Nowadays, one has to wonder the motives behind forcing a userid to a specific device.
The three steps listed above provide a method to clean this feature, and let you log out and log into different accounts.