Which directory?

Yesterday I downloaded and installed Mozilla 1.6. It works perfectly and I'm pleased so far. The program currently resides in my home directory. I have the feeling (don't know why) that this isn't a good idea. So my newbie question: is there a specific directory where programs such as Mozilla should be stored after installation? Something tells me that there is some kind of convention or protocol in Linux as to where folders from new installations should reside. I would appreciate knowing if this is true, and why it might be true. Rem