Well, the easiest way would be to just reinstall the program (download the installer / program) and place the downloaded file in a dedicated folder on your HDD called "Installs" or something. From there, open the installer and it will ask you where you want to install it. Default will be C/ which is your boot drive and SSD. You will want to browse to your HDD - whatever letter it is assinged D:/ or something. And then choose the install location within there. So, for example, D:/>Program files > Mozilla > Mozilla Firefox browser.exe.