Need help regarding my macbook overheating?

I have a black 13” macbook running leopard and it is often running very warm, typically about 70 degrees or higher and the fans are working and very loud. I will manually blow in the vents for a few minutes and this will usually help bring it down a bit but it will usually get hot again a few minutes after stopping.

This will occur even when firefox is the only application I’m running. Any help would be great. Thanks!