NotAwesome is simple to use. When adding a bookmark, just check the box labeled "Hide from AwesomeBar Searches." It's that easy for editing existing bookmarks too. NotAwesome is still in its early stages of development, so this is really all it does. However, new versions will likely include more customizability, such as a feature to allow mass bookmark hiding already mentioned by the developer. NotAwesome isn't a comprehensive privacy tool by any means, but it is a good solution if you're only worried about a few bookmarks.
Note: This is an experimental add-on for Firefox. To install it, you will have to check a box saying that you understand this.