There are several ways to achieve desirable results in Firefly.  To recreate a natural lighting effect, you can incorporate a Diffuse IDL with a light probe HDR.  There are several different types of probes to encompass unique times of day environments.  Using a skydome to illuminate your scene does not need to be visible.  It's like using an offstage lamp, you are providing a variable light situation.  Snarly's EZDome can be modified to the extent that the inner dome can be black and the outer dome provide only the HDRI lighting.  

But you are rendering a comic-style scene, so realistic lighting doesn't apply to this situation nor do you need it credible.  Use an infinite light or diffuse IDL and adjust the brightness to your liking.  Probably has a dim intensity so your flame becomes the predominant light source without increasing over-exaggerated shadows.  Use a point light for the flame and set its attenuation to Inverse Square, you want the light to fall off with distance drawing attention to the combatants in the scene.  Simplify the lighting scenario, no need to make it complex just for a comic page panel.