I'm trying to locate where the Ubuntu Software Center is to choose as default for handling APT links in Firefox. I can click on the links, and I get the pop-up, but Ubuntu Software Center is not there. I tried to choose an application through Firefox's settings and through the pop-up, but I don't know the path. As you can see by my screen shot for the pop-up I chose the wrong one as that doesn't work. What is the correct path I need to select the correct file?

EDIT - I added a fourth screen shot. I don't have it in that location. This is what I have. My view is in ABC order, and it's showing hidden files.

![USC1](https://i.stack.imgur.com/wNLYO.png)

![USC2](https://i.stack.imgur.com/GqBLD.png)

![USC3](https://i.stack.imgur.com/uaqn3.png)

![USC4](https://i.stack.imgur.com/TeH83.png)