Like the title says, I've observed a strange interaction with the two exotics. If you score enough multikills with a Firefly explosion, you'll trigger the Burning Steps' Flamewalker buff, which seems to simultaneously also activate Memento Mori, or at least the visual and sound effects associated with it. The effect also happens to match Flamewalker's duration, though I haven't found a nice consistent environment to test whether or not the damage values match one-for-one. It could just be an Audio/Visual bug, but I'm not sure if it would have any serious implications is it really is triggering some kind of Rampage version of Memento Mori.