Fire Glitch

So the Fire Glitch, one day I was playing Minecraft and I saw a light. I had no idea what it was, but when I went up to it, I was on fire. So I placed a block under it and it showed fire. How to do this glitch? Turn fire spread off, place a block, use a flint and steel or fire charge on top of the block and break the block. Then, you have invisible fire. Perfect trap.