Polymerfire Firebase Firestore mixin - sorting

Question

I have a Polymer property using Polymerfire Firestore mixin and a dom-repeat:

        mySections: {
                    type: Array,
                    collection: '/users/{user.uid}/sections',
                    query: (q, el) => {
                             q = q.orderBy('sectionName')
                             return q;
                           }
                  }


<template is="dom-repeat" items="{{mySections}}" as="Section" index-as="SectionIndex">

    {{Section.sectionName}}

</template>

However, it's not sorting on sectionName? What am I doing wrong? Am I missing something here? Thanks.