OK so I just reread what it said.  Never really says which tank hit with the rounds.  At first I thought the tiger hit the firefly...now it looks like the firefly hit the tiger.   
Read it one more time.
There was no Firefly involved in this encounter.
3 Shermans, 1 Tiger, 1 17 pounder anti-tank gun.  The Shermans engaged the Tiger.  Tiger Kills one Sherman.  17 pounder set up 3,000 yards away, engages Tiger.  Tiger turns face on (90 degree turn) to anti-tank gun.  Facing the threat with it's strongest armor.  Tiger is hit 2-4 times, ineffectively due to the great range.  Shermans move back up to within 500 yards of Tigers flank and engage.  Tiger withdraws.
What I gat out of this is:
1.  Tiger kills one Sherman from 500(?) yards.
2.  17 pounder anti-tank gun is ineffective from 2,400 yards against the front armor of a Tiger.
3.  A (regular) Sherman's gun is ineffective against, or missed, a Tiger's flank from 500 yards.
wrongway