Think this has been fixed (Destiny)

by ChrisTheeCrappy, Monday, April 06, 2015, 13:49 (3310 days ago) @ CruelLEGACEY

Pretty sure this was a bug they fixed but didn't mention when it was updated.

Basically as Funk mentioned somewhere else, the total damage is not increased, as the explosions just add back up to a normal head shot. But if that enemy died from the last bit of that headshot then the explosion would kill them. If the headshot is what kills them it gets triggered (but now the Headshot does less Critical damage). What the error was before, is I noticed if I still had to shoot someone a second time and they had little health, Firefly would not happen on the second shot even though it was a headshot. My belief is that they calculated the explosion damage BEFORE the Headshot/Critical damage, so that way they didn't Firefly if it was on a second shot. I believe they fixed that now, as I have seen it happen a lot more consistently on my second shots.

Of course other items could be that they didn't count the Crit as Crit damage, or I am just crazy. Crazy is possible.