Molten strike not showing up in skills? Help

Ok so I have molten strike and fire trap, each of which I've been using fine. Now, all of a sudden when I place the molten strike orb in an item it doesn't show up in the skill slot. But when I place a fire trap it fills both slots 2 and 3, I don't understand.

Even placing molten strike all by itself the skill doesn't show up. I'm really confused.

Nevermind, figured out I need to click the empty skill slot and just choose it. Sorry, newb here.

Click on the right mouse button skill box in lower right of screen, choose molten.

Yeah, dumb newb question :) But thank you for the reply.