You can work with multiple accounts at same time by using Multifox for firefox or Multilogin for Chrome. Through these extensions you’ll be able to log into more than one Gmail, Facebook, Twitter, Dropbox, Tumblr, Instagram, Skype etcetra websites.
Log into multiple accounts
Surely you can use the private browsing or incognito mode to do that but using these extensions will make things easier. Gmail users also have the built in Google Account Chooser feature too. However, Microsoft, last year stopped supporting linked accounts for Outlook last year.
Multifox for Firefox
Multifox is a Firefox extention that will let its users to connect to websites using different usernames, at the same time. i.e., If you have more than one Outlook account you can log into multiple Outlook accounts simultaneously and open all of them at the same time, without interfering their individual operations. Extension for firefox : Multifox.
MultiLogin for Chrome
MultiLogin which is a chrome extension does so in a similar way as it adds a button to the browser address bar. Using Multilogin, you can log into multiple accounts on the same site at the same time.
Extension for Chrome: Multilogin