How do I open a file as a separate window by default?
Open Preferences
Click menu SnapGene → Preferences (macOS) or menu Edit → Preferences (Windows or Linux).
Select "General" in the sidebar and check the option to "Open files in separate windows by default".
Alternatively, to open Preferences, click the Cog button in the top toolbar (SnapGene 8.1 or later) and choose Preferences.