Last time I checked, ecstacy is usually how it is called when in pill form, with the idea that it is not pure MDMA. That is, it may be cut, a combination of drugs or something else entirely.
MDMA/molly is usually in crystal/powder form, with the idea that it is more pure.
But how drugs are called on the street and what they are in reality is constantly changing, there are countless myths, and dealers are not exactly a reliable source of information regarding what they sell.
In reality, that's essentially the same thing. If you look at https://www.drugsdata.org/ you will see that it is mostly just MDMA, the form doesn't matter much.
even though MDMA is the real technical name (and Molly + Ecstasy are nicknames), the name "Ecstasy" is kinda misleading because it's usually MDMA mixed with other stuff, and that's not always good...
the name "Molly" has a pure vibe to it. It's like a warm hug from a friend.
Dr. Andrew Huberman said in his video that MDMA is not actually ecstastic, rather it produce warm feelings and promote inner acceptance and peaceful connections with others.