A submarine surfaces with the aid of compressed air. In the same way a compressed hydrogen cycle could both regulate lift and feed a fuel cell in a lighter than air vehicle. Helium would still be used as the main lifting gas. Solar power cells could provide power for the generation of hydrogen from water via electrolysis. These are all just improvements to an existing proven mode of transportation. The real novel idea here is the mission of the airship.
Very experienced pilots are needed to fight wildfires with conventional fixed wing aircraft, and the accurate placement a relatively small amount of flame retardant and/or water is crucial. The job is dangerous and stressful. A lighter than air ship with a suspended gondola which is fed water and/or foaming agents, and hoses supported by semi-autonomous ducted fan extensions (similar to drones) could be the solution. A vehicle as described could allow for safer operation, larger water payloads, and more time on station.