A fire extinguisher in a dream signifies wish fulfillment. It means that the dreamer is tired of dealing with every day problems and wants relief.
The dreamer might be feeling disheartened and burnt out, but their dreams with fire extinguishers could signify that they will soon receive help they need. They may also have some kind of job or task that is overwhelming them, but the dream has come to show them that this is not the end of the world and to keep pushing through because it will bring relief in the end.
Also, the meaning behind fire extinguishers in dreams is that they represent the need to put out some kind of fire. This can be either emotional fires or actual fires.
For example, a very emotional person dreams about a fire and grabs a nearby fire extinguisher, perhaps to put out an emotional outburst that has not yet happened. Or a person who has been through a traumatic experience in the past dreams about being near a fire and grabbing the nearest fire extinguisher before he or she is hurt again.