Why are the fields for under "User Agent" not highlighted?

[iMore Question]

Aloha, I am trying to get IE SItes to work on our MAC. Followed the:
Safari>Preferences>Advanced>Show Develop>User Agent.
Field Choices or prompts are grayed out, I am not able to choose from the list. Please advise. Thank you very much for all of your great and useful info.

 

[kch50428]

Did you restart Safari after activating the Develop menu? Try that... and try restarting the Mac...