What are the main differences between Forex trading and stock trading?

Stock trading is much more heavily regulated than Forex trading. It is much harder to obtain clearance to use leverage or sell short in the stock market. Since Forex trading uses pairs that are pitted against each other, short selling is a natural feature of the market. Stock trading is also only possible during a very limited window during the week, typically during the business hours for the country or region.
Unlike the stock market, where you can hold a stock and let it ride in value over a long time, Forex is generally more volatile and such passive strategies are not realistic.