What is the ruling on buying and selling foreign currencies on the global stock market by monitoring price fluctuations via a computer screen?

There is no harm in buying and selling foreign currencies on global exchanges if they are free from Sharia prohibitions such as usury (riba), gharar (ambiguity or excessive risk), jahalah (ignorance or lack of clarity), deception, or fraud. It is a condition that possession (qabd) takes place at the time of the transaction (possession at the session). If the transfer or sale is in a single currency, then equality (tamathul) is necessary, and disparity (tafadul) is forbidden. However, if it is between two different currencies, then there is no harm in disparity if possession takes place in the same session.