How can you set a preference that is local to your machine?

You have a requirement for an incident workspace where clicking a kind of text hyperlink should open a browser window by using the third-party URL of the loaded client. You want to implement this by using add-ins.
Which add-in should you create?

Your customer has created a new script and deployed it to the agents in the call center within incident workflows. However, the script hangs on execution.
Identify two reasons for this.