Bounties attract serious brainpower to the challenge.
My idea is to use fire retardant material to build pieces of a collapsible and portable wall to help contain wildfires.
Firewalls and barriers are a common feature of any modern building yet I have not found any instances of portable walls being used. I'm certain that if we can get this idea functioning on a large enough scale it would be able to help fight wildfires by stopping the spread and perhaps even acting as a barrier for the wind.
Ideally, the walls would be able to expand telescopically in order to save space. It can be compact while being transported and then "unfolded" when needed. Even at a small scale of up to 2 meters tall, they would help, but if we can get them to be raised to around 10 meters they would also have a significant impact on the wind.
Regular firewalls are usually made of concrete, but there are more options, like treated wood or Geobond or even glass.
These walls could also be designed around firefighters' needs, for instance, there could be mechanically operated hoses or sprinkler systems fitted on the walls.
The most effective solution would obviously be permanent fixtures, but we don't want to wall off our mountains, plains and forests permanently, with this solution, these walls can be installed quickly when a fire breaks out in order to hopefully help contain it. The pieces can be kept in storage facilities at the fire department, or near high-risk areas.