Microsoft Word
1. Click on File->Print. Change "Print One Sided" to "Print on Both Sides (Flip pages on long edge)
Firefox
1. In the print dialog, click on 'More Settings'.
2. Click on the "Two-sided printing" option. Select "Flip on long edge", and click OK.
PDFs in Adobe Reader
1. In the print dialog, click on Properties.
2. Click on the "Printing Shortcuts" tab. Select "Two-sided Printing", and click OK.