Toggling bookmarks are extremely helpful. You have to jump from file A to file B, over to file J, back to B, back to A. (Sound familiar to what you did today :) – Bookmarks are little popcorn nuggets you can leave along your trail to find your way back to where you once were quickly. Bookmarks are controlled from the Edit | Bookmarks menu, or fully from the keyboard. This video introduced you to bookmarks, and then shows you how to change the look/feel and visibility of the bookmarks.