When you are at a location you want to bookmark, click on the bookmark icon in the menubar. The bookmarks page will open. However, the active URL stays the same in the address bar. Drag the icon of the site from the address bar to the bookmarks page. As you drag over folders, they spring open. There is also a line that appears below the cursor to indicate where the bookmark will be placed.
When you're done, just click the Bookmark page icon again to close it and return to the page view.

