Up until now, I was under the impression that person B ratted on person A to person A's employer. Now it appears that person B went beyond that and went to great lengths to have person A fired. Which is correct?

Uhm...if Person 'B' goes to Person 'A's employer (and I don't believe that 'b' works for 'a's employer), what OTHER reason could there be for ratting out??? I think it is unrealistic to assume that 'B' would not know the consequences for 'A'.