Metamask is a browser extension available for Google Chrome, Opera and Mozilla Firefox. This extension allows you accessing Ethereum enabled applications and sign transactions to interact with the Ethereum blockchain.
MetaMask also allows you to create and manage different identities: each time that Ethertify needs to perform a transaction and write to the blockchain, you will get a secure interface to review the transaction, before approving or rejecting it.
You can create several accounts with metamask and switching among them at anytime. Ethertify profiles are associated to one account and, in the case of Entities, the account needs to be unique. You do not need to worry about signing a transaction with the wrong account. Ethertify will warn you and the operation will not be allowed.