If you have noticed, you can never open more than one Facebook user
account simultaneously in any browser. One way around this is to use the private browsing feature, but this will only let you open 2 accounts at the same time and fails if you try to open any more.
What if you need to log into more? Well, this article will tell you how to log into many Facebook accounts with a simple script.
Installing the ScriptIf you are a Chrome user, you can use the script directly, but if you are on some other browser, make sure your browser has the necessary add-ons, like Greases Monkey is required for Firefox, before you proceed.
Once you have everything in place, install the Facebook Switch Accounts script in your browser and restart it.
Click on Add Accounts under the Switch Account menu and add all the accounts you work on simultaneously.
Now, all you have to do in order to switch accounts is click the Switch account button and select the nickname of the account you want to switch to.