Molly is a slang term that refers to MDMA. Molly is a powder form of MDMA and is often in capsules. Ecstasy is another street name for MDMA and usually comes in tablet form, although some individuals may crush and snort them.
Molly and Ecstasy can look a little different, with Ecstasy coming in small tablets of varying colors that can inadvertently be confused for candy. While Ecstasy contains MDMA, Ecstasy tablets are often laced with other substances.