At present it will use whatever the OS default is, it would be nice to be able to custimize this within Plastic, e.g. a simple table of file extension versus application (don't forget to allow for files with no extension, e.g. INSTALL, README, etc). This would make life easier fot instances where no defaul is even set (e.g. my Linux VM), and also cases where by default I want to edit files in Plastic but run them in my OS (e.g. script files).