Place your mouse cursor in the box and click your left mouse button. A tick
mark or dot (depending upon whether it is a box or a radio button should
appear. Check to see if you need to click the 'Apply' button before exiting.
If you have dismissed the prompt dialog box that appears when you initiate
a download from the internet, you can bring it back. Open Files Options>
File Types. Select the file type involved. Click the Advanced button.
Towards the bottom of the screen that appears, place a check next to
"Confirm open after download." Click OK on this screen and the next (you
should be back at the screen with the File Types list for this second OK).
