Many people still confuses these two units, and more now that MARSOC are being relevant in the media. Truth is that some Force Recon joined MARSOC's lists, but they yet are different units.
Force Recon is a reconnaissance unit from US Marine Corps, the elite unit of Marines until the creation of MARSOC. They're specialized in special missions and intelligence collection. They've been active since 1957 and count with more than 400 people in their troops.
The US Marine Corps Forces Special Operations Command o MARSOC is a unit created in 2007 as a contribution to USSOCOM (entity that holds the main special forces units from the US). They train to carry out Direct Action missions, special reconnaissance and training of other foreign units among other tasks.