This will probably have more info than you want, and I apologize in advance...
Whether you have pills, powder, or crystal, you should always test your product.
You can get test kits from Dancesafe, EZ Test, Bunk Police and other suppliers.
In a perfect world, MDMA pills and "molly" both contain MDMA and only MDMA. However, sadly, it is not a perfect world.
Pills and molly can both be adulterated with known and unknown compounds. They may be intentionally adulterated (example: your dealer sells you Meth instead of MDMA), or unintentionally adulterated (example: the chemist doesn't know what he is doing, and weird chemicals are left in the MDMA).
Even if you are fortunate enough to have powder that appears to be MDMA, there are variations in the purity and quality of MDMA that is available.
If you plan to do MDMA in the future, I recommend you invest in a small gem scale in addition to the test kit so that you can experiment with your doses and find the perfect dose. 120 mg is a good place to start.