I'm thinking like storing a token somewhere on the browser and do so comparission.
For example, you login on browser1 and the token is token1, store it on your db with the userid.
Every page load/action (even on login step), it first check to the server (db) if there's another one, and if the same user has another one (token2) it means has logged on browser2 then return logout where there is a token1