I was willing to call it a typo. Obviously the writer for Yahoo! DIY knew how to spell fiery. She was just a little clumsy when typing out the headline:
Then I noticed that she didn’t know that the thing over a fireplace was a mantel. Then I noticed a repeated firery. This time it had to be intentional. She really thinks that’s a word! Just like she really thinks that an ellipsis is made up of six periods, and not the customary three.