The flame of a fire produces light and heat and often flickers or dances. As a verb, to flame is to be on fire or to flare up.
On the Internet, flame has a different meaning: to post or send aggressive, negative, or insulting messages in a public electronic forum. "Flame wars" are exchanges of such messages between individuals or parties and often occur behind a veil of anonymity. It's an appropriate term, given that inflammatory, which takes flame as its root, describes speech or action that tends to incite a heightened and negative response.