When you print documents from ShipStation (labels, packing slips, etc), a printer dialogue box will display your printing options. These options are user specific and saved in your browser, so each of your users and each of your workstations can have different printing defaults.
You can specify your default "Print to" printing methods per document, per user on your account, and per browser in two ways...
The first way...
In the print dialogue, check the box to Remember my selection and always do this for this type of document before selecting your printing option.
ShipStation will remember your setting and skip this popup going forward. However, you can change this at any time in your Printing Account Settings (as shown in the second way below).
The second way...
Click Settings (the Wrench icon in the upper right).
Next, select Printing and then Printing Setup from the sidebar on the left.
Click Always Prompt from the Print To column.
Select how the documents print by default:
Remember, each user can customize their default preferences for each browser and workstation they work from. So you could, if you wished, have different default settings for each user, workstation, and browser that accesses ShipStation.