Safari has an option to automatically open files that are considered "safe". Usually these are document types (e.g. PDF) but sometimes it may become necessary to add other file extensions that are not considered "safe" by default. This can be achieved easily by adding/editing a plist configuration file to your profile (i.e. user-based setting).
The preferences file is located at ~/Library/Preferences/com.apple.DownloadAssessment.plist, and determines whether a specific file extension is considered safe or not.
If the file does not yet exist, create it with the contents below:
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.ap ...