Make Adobe Reader the default application

opening pdf files in Mozilla Firefox's browser:

Step 1:

Click the Open Menu icon in the upper right-hand corner, opening the menu options box.

Step 2:

Click on the Options icon inside the menu window

Step 3:

In the left hand column of the Options Menu, click on the Applications icon.

Step 4:

Click the application in the Content Type column and choose Adobe Acrobat / Adobe Reader as the (default) application in the Action column.

Close the Options window/tab to implement changes.