From Google result it looks like AngularFire used to have a orderByPriority filter. But I cannot find this in the current AngularFire api docs: https://www.firebase.com/docs/web
There is no longer a need for orderByPriority
since you can utilize a synchronized array, which is already implicitly ordered.
So in ancient days, you would do something like:
$scope.data = $firebase(ref);
<div ng-repeat="item in data | orderByPriority" />
In not so ancient times (i.e. 0.8.x or greater) you would simply choose an array format:
$scope.data = $firebase(ref).$asArray();
<div ng-repeat="item in data" />