You can use collection('...').where() to filter.
Inside the where syntax, you will fill the field and comparison.
For example, if I want to filter the USD currency, I use:
db.collection('money').where('currency', '==', 'USD')
The .where() comparison worked for me, but I had to allow firebase to create indexes for different fields. I assume that the indexes are necessary to compare whatever field you are using in the .where()