Hey Ken,
Firebase will by default maintain a connection indefinitely. To close the connection manually, you can use "Firebase.goOffline();" This will disconnect all Firebase instances within the process though, so depending on how your microservice architecture works, I don't know if this will be appropriate (maybe you can explain more).
Another option might be to just use our REST API if you're just making one-off read/write requests in your micro service code (i.e. you don't need event subscriptions). This will avoid having long-lived connections entirely.
There's no way to clear all concurrent connections for your Firebase. You'll need to figure out what's connected and disconnect it (e.g. kill all your microservice processes or whatever).
Hope this helps,
-Michael