Jack - I don't have the mod, but here is how you would fix the problem.Don't know why the firing mod doesn't work. I have been trying to figure that one out also.
Check to see if the mod has a gfx file, and not a unitgfx file.
If this is the problem, then just copy the unit infomation from the gfx into a unitgfx .
If this is not the case, then I'm at a loss as to the problem, but this is how I updated my firing-mod files.
davinci