  We continue our studies of burn-off chip-firing games from [Discrete Math.
Theor. Comput. Sci. 15 (2013), no. 1, 121-132; MR3040546] and [Australas. J.
Combin. 68 (2017), no. 3, 330-345; MR3656659]. The latter article introduced
randomness by choosing successive seeds uniformly from the vertex set of a
graph $G$. The length of a game is the number of vertices that fire (by sending
a chip to each neighbor and annihilating one chip) as an excited chip
configuration passes to a relaxed state. This article determines the
probability distribution of the game length in a long sequence of burn-off
games. Our main results give exact counts for the number of pairs $(C,v)$, with
$C$ a relaxed legal configuration and $v$ a seed, corresponding to each
possible length. In support, we give our own proof of the well-known
equicardinality of the set $\mathcal{R}$ of relaxed legal configurations on $G$
and the set of spanning trees in the cone $G^*$ of $G$. We present an
algorithmic, bijective proof of this correspondence.
