Q. I read on the internet that fired, meaning dismissed from a job (he was fired) came about in the 18th century when landowners burned down tenants' houses rather than pay taxes on occupied land.
A. The internet probably has more language myths than realities, and this is one of them. The Oxford English Dictionary tells us that fired in this sense is American slang. It means "To turn (anyone) out of a place; to eject or expel forcibly; to dismiss or discharge peremptorily; to reject (a picture sent in for exhibition). Frequently with out."
1885: "If the practice is persisted in, then pupils should be fired out."
1887: "Postmaster Breed says the next time such a thing occurs he will fire the offender bodily."
The context here suggests firing from a cannon rather than torching a house. Discharge shares the same duality: it refers to firing a gun and firing someone from a job.