To change what happens when you double click a file:
Choose Transmit > Preferences...
Click Files
Choose an option from the Double Click Action popup
Do Nothing: Double clicks on files are ignored.
Transfer: Double-clicked local files will be uploaded. Double-clicked remote files will be downloaded.Edit: The double-clicked file will open in Transmit's built-in text editor.Edit in External Editor: The double-clicked file will open in the default editor application for its type.