EDIT: As mentioned in the comments, the docs link is currently dead. This project might be abandoned. Please try the next answer.
EDIT 2: I removed links to the software and docs since it looked like some phishing website took over the domain.
Original answer:
Check out Firebase Admin. It's a UI for Linux, OSX and Windows and it has a Query tab that lets you experiment with queries.
Read the docs on how to create the private key the app needs to connect to your project.