Firefox with Greasemonkey: Free Greasemonkey user script Google Account Multi-Login adds a simple drop-down menu to Google pages (including Gmail) for quick switching between your different user accounts. Just install the script, reload the page, and you can start adding your Google accounts to the drop-down. It's simple to use and it's a huge timesaver for anyone who actively uses different Google usernames and passwords. It's probably not the most secure place to put your passwords, but if that doesn't bother you, this script may come in very handy. The Google Account Multi-Login script is free, requires Firefox with Greasemonkey.