Use the down arrow to enter the dropdown. Use the up and down arrows to move through the list, and enter to select. To remove the current item in the list, use the tab key to move to the remove button of the currently selected item. Use Escape to close the dropdown and return to the search box.
Navigate Categories by tabbing to the major areas. Use the Down key to open the subcategory and then use the Down key once more to enter it. Navigate the subcategory using the Up and down keys. Once on the subcategory you are interested in. Use the Enter key to navigate to that page.