It's not very hard to pop all of the pigs but watch out for the flying debris blocking your path in the way. If not, you'll not be able to pop Hekto Porko at the far-left.
Explode the all 3 stone block corners and also the far-left corner is the key for 3 stars.
First, shoot the Firebomb Bird to the top-left corner, explode by tapping the screen when he's above one of the 2x2 groups of stone square blocks. This should make the stone blocks to fly downward and explode the TNT in the bottom-left corner. Now, we just need to explode the top-right corner to get enough score. So, fling the second Firebomb Bird to the top-right corner and explode by tapping the screen when he's really close to the corner. Don't destroy too much blocks because that'll waste your points and decrease the chance to pop all pigs. Now, we just need to pop the remaining pigs and Hekto Porko. If Hekto Porko is the only pig remaining, so fire the third Firebomb Bird to a path with no debris into Hekto Porko's corner and then explode (if the path is not clear, so use the third one to clear the path first, then use the fourth one to pop Hekto Porko). Hopefully the debris will pop Hekto Porko. If there are more than one pig after the second shot, so fire the Firebomb Bird into the middle and explode to throw debris into piggies and clear the path to Hekto Porko. Then fire the fourth Firebomb Bird into the middle of the middle-left corner and explode Hekto Porko.