Visit the web site or bookmark it. That drop-down is generated from your saved bookmarks and web page visited history.

I tried that. Didn't work. I already have a few addresses in the drop down. Not the max amount. I just want to add a few more to the drop down

Do you mean the arrow at the far right side of the location bar or what you get if you start typing in the location bar?

The list that shows if you you click the arrow at the far right side is a most visited list based on URLs that you typed in the location bar. If you want some to disappear then you need to remove them from the history and visit sites that you want to see a few times until they appear.

You can make the Visit Count column visible in the History and Bookmarks Manager (Library, Bookmarks > Organize Bookmarks, Views > Show Columns)