Is it possible to use the REST API to push an event to a list (via an HTTP POST) and also specify the priority of the item that is being pushed? Perhaps as a field in the JS
Yes! To post data with a priority, you can use:
var myObj = JSON.stringify({name: 'My Name', address: 'My Address', '.priority': 123});
$.post('http://demo.firebase.com/demo/testing.json', myObj);
If you want to post a raw value (e.g. "hello") with a priority, use:
var myObj = JSON.stringify({'.value': 'hello', '.priority': 123});
$.post('http://demo.firebase.com/demo/testing.json', myObj);