Normally it is not possible to open multiple Gmail accounts simultaneously using Internet Explorer 8 browser. Therefore, when you are logged in Gmail, you can’t open another Gmail account using another tab or window. Because whenever you try for logging another account, it will automatically open the first login ID.
If you will use different browser means you can login multiple Gmail accounts simultaneously. If you still want to utilize the IE8 to use multiple accounts means here is the perfect solution by altering the default browser. The name of the feature is NoMerge, which can bring the finest solution for you.
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