Welcome To Gmail
I’ve tried this little Gmail Login Switcher tool this morning and I must confess that it really made me happy. It allows you to instantly switch among all your Gmail login accounts without having to log out from the account you’re logged in and then re-log in to the other account (very annoying if, for any reason, you have to check your email frequently).
Actually what this script does is replacing the “Sign Out” link located in the upper-right corner of the Google login services with a drop-down menu. From that menu you can select one of your alternate Google login accounts, and it will immediately logout and login to the other without any other user intervention.
Even if, once installed and configured, using the tool doesn’t require any particular ability, the installation process can put in little troubles the average internet user. Then, let’s show it in details.
Gmail Login Switcher Requirements
First of all, you must have all the following things in place:
Firefox. Sorry, the tool only works on Firefox. If you are still following the Explorer, listen to me… leave it alone, join the Fox crew and don’t look back: it’s free, smarter …and you won’t regret it!
The new version of Gmail. If you are still using the old version, you will have to switch to the new one. It’s easy: login to Gmail and click on the “Newer version” link on the upper-right corner of the page. Then logout and repeat this operation for each of your Gmail accounts.
Greasemonkey extension installed. This will probably sounds a little exotic for most of you. Don’t worry: Greasemonkey is a Firefox add-on that “allows you to customize the way a webpage displays using small bits of JavaScript” - just to use their own words. Well, install it and forget it! Go to the Greasemonkey homepage , click on the ‘install’ button, confirm that you want to install the add-on and restart Firefox.
At this point you will see a little monkey face on the status bar (lower-right corner of your Firefox window) 
If the monkey looks sad and grey 
, click once on the icon to activate.
Installing the Gmail Account Multi-Login script
Now that everything is in place, you can install and configure the script itself. Go to the script homepage and click on the black button on the right. Once again, Firefox will warn you, but go on. Done!
Configuring the Gmail Login etc.
Now that you have the script installed, login to one of your Gmail accounts and manually add all the Gmail accounts among which you want to be able to switch. To help you to do that, I’ve uploaded a short instructional video on YouTube. Hope this help…
Once finished with adding all your accounts to this Gmail login tool, you will be able to switch from an account to another simply selecting them from the drop menu.
Enjoy!