The same things happens. However, it does work sometimes but I can't isolate the circumstances under which it works. When I first got your message it worked but then it didn't when I retried it later.
I have my firefox set to clear just about everything when I exit it. This includes history and cookies and stuff. I wonder if that could be related.
EDIT: Middle-click to open works fine roughly 1/5 to 1/10 of the time. Tested this by middle-clicking the bell a bunch.
Are you looking for something to play with your Dad or something for your Dad to play with other people?
Terraria is great if you want to play with your Dad. The basic controls are simple and you can help with the complex parts of the game.
3D games tend to be difficult for old non-gamers to learn. They have a lot of trouble moving the camera and moving themselves at the same time. This includes first-person 3D games like minecraft. If you watch old people play they wind up staring at the floor or sky a lot. 2D games are usually easier to start with.