Techniques are described for associating file types with application in a network storage service. User environment manager at storage service receives file identifier for specific requested file from user operating computing device and obtains file format type identifier associated with file identifier from data store for file. User environment manager determines default application to open specific requested file in response to matching application ID (app ID) from default “Open with” list contained in user preferences store with list of app IDs for installed applications that support file format type. Once determined, user environment manager opens specific requested file from data store utilizing the default application. This Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.