The few differences I can think of are :
there are thousands of stocks while there are few currencies to trade in the forex market
in stock trading, you have to research a lot. But in forex, once you understand the currency patterns, it is just a repetitive automation job to trade them.
you have to buy stocks in order to sell them. But in forex trading, you can sell currency pairs even without buying them
it takes a lot of time to get good profits(200–300%) in stock trading. While in forex you can even earn millions in a matter of time (provided you know how to do it)
your stocks would rarely go below zero. But with forex you can go negative or bankrupt within a matter of few seconds. :)