It's a "suppression capacitor", used to reduce EMI emissions onto the line from whatever that breaker is feeding. Things that create a lot of EMI (Electro Magnetic Interference) will turn the incoming line sources into antennae, blasting that EMI into other things that are connected to the same source. My guess would be that this breaker is feeding something with a Switch Mode Power Supply of some sort that does not have it's own EMI suppression built in, and there are some EMI sensitive devices elsewhere in the facility. I'm going to guess it's at a hospital or other medical facility (or given your location in Florida, a nursing home...)
Over the years rules have changed and most SMPS based equipment is now required to have it's own EMI suppression in order to get approval from the FCC (for the US) or CE (for IEC countries), but that was not always the case.