Automated way to add “All Listings”
Using version 2.6 or higher of the theme, you can add the All Listings item to the menu. See the demo to see how it’s implemented. It’s tucked under the “Browse By” menu. Go to Appearance -> Theme Options -> Browse By… Make sure the “Browse By” menu is enabled, and also the “All Lisings” is enabled.
Manual way to add “All Listings”
If you want to add “All Listings” in the menu, but NOT tucked under the “Browse By” menu, then you must add the “All Listings” to the menu manually…
First, you will need to find out the URL that goes to the All Listings page. To do this, first enable the ‘Browse By’ menu item (Appearance -> Theme Options -> Browse By). Also in that section, be sure to enable the “All Listings” item.
Visit your site, and mouse over the Browse By menu item, and also mouse over the “All Listings” menu item under it. Right-click All Listings and Copy the URL to the clipboard. (This is the URL that is for my demo: http://www.informatik.com/themeforest/openhouse2/search-results/?alllistings=true)
Now, add this URL as a custom menu item. Go to Appearance -> Menus, and on the left side, add a new custom menu item. Paste in the URL and give the menu item a name. Add it to a menu and save.