Yes, salt water can be used to fight forest fires. Then, after the forest fire, you plant alfalfa or Alaskan Lupine to absorb the salt and then plant trees a couple of years from that point.
It may not be rocket science, but it is know how to regrow forests, in the event of a fire.
Somebody tell Michael Bloomberg.
There are salt loving (tolerant) plants which can grow on shores or on salty soils (saltcedar and cabbage come to my mind).
And, Getting salt out of the soil is not rocket science, just flood the area with fresh water and sooner or later you will fix the problem. Farmers in Australia are farming on pretty salty soils, and somehow manage.
Romans ceremonially plowed over places like Jerusalem and threw some salt over it, but these places recovered pretty quickly, it was just for a show.
Salt water is corrosive, but heck, there are boats sitting in ocean for years.
In summary, they could and should use salt water in LA.
They are using it now, but somehow were not in the beginning. I heard rumors that they were needing permits?!?
Also, coastal plant life is very often more resistant to salt water, salt spray, and so on, than are some of our inland species.
BTW, my Dad was a lifelong Forestry Professor. He could talk all day on regrowth strategies! Fire prevention and woodland, grassland, etc., firefighting, too... :-)
Hurricanes Helene and Milton both caused significant storm surges in coastal areas. Unfortunately, most plants impacted by saltwater flooding will not survive. The plants sprayed by sea water to put out the fires will end up as dried up vegetation that needs to cleaned out before the next fire uses it as fuel to become a wild fire.