When you sign into a website, your login information is stored in a text file called cookie which remains active till you are signed in. Therefore, you cannot login into another account from the same service provider at the same time until you log out from the site and the cookie is cleared. In this guide, I will show you how to login/sign into multiple instances of websites and emails accounts from the same service provider at the same time without logging off or signing out using Internet Explorer, Opera or Mozilla Firefox.

Method I for Mozilla Firefox users:

There is a great addon called CookieSwap which allows you to create and manage ‘profiles’ of cookies that you can swap in real-time, allowing you to sign into multiple instances of the same website or webmail without logging off.

After you download and install CookieSwap, you will notice a new CookieSwap profile icon at the bottom of Firefox. Whenever you want to sign into another instance of the same service, open a new window or tab, right click on the CookieSwap icon, choose the cookie profile and then visit the website.
By default, there are only three profiles. To add more cookies profiles, navigate to C:\Documents and Settings\{username}\Application Data\Mozilla\Firefox\Profiles\u8iiyrst.default\CookieSwap and create a new file called cookies_Profilen.txt where “n” is the next profile number in sequence. Make sure you restart Firefox after adding new profiles.

Method II for Internet Explorer, Opera and Mozilla Firefox:

This method takes advantage of the Run As function of Windows OS. Basically you need to create multiple Windows accounts (Start—>Run—>Lusrmgr.msc) and then launch any web browser by right clicking on the browser executable and choosing “Run As…”. Any cookies launched using this method are saved under the profile of the user with whose account you ran the browser.

To always launch your favorite web browser using Run As, create a shortcut of the executable to your desktop. Right click on the shortcut and go to properties. Click on the advanced button and check “Run with different credentials”