To display each new Event as it happens across all accounts that have given you permission to View, add the toast URL parameter like this:
The value 3 is the number of seconds to display the Event. Use a value of 0 if you prefer that the Event remain visible until explicitly closed.
NOTE: This Event Streaming maintains PubSub websocket connections to all clients to continually fetch new results as new Events arrive, so it's an add-on feature that must be enabled at the domain or account level. Contact your integrator for information.