This extremely simple extension lets you navigate up a web site’s hierarchy, step by step, by typing ⌘⌥↑ (that’s Command-Option-Up).
Say you’re viewing the page at www.apple.com/support/lion/. Navigating up the hierarchy means going up to the “parent” of the current page, so that would get you to www.apple.com/support/. Go up again, and you get all the way up to www.apple.com/.
Safari actually has a built-in way to navigate up a site’s hierarchy. To activate it, ⌘-click the page title in the window’s title bar, and then select a “path” in the pop-up menu. It’s just like navigating up in the Finder. This extension just provides a handy keyboard shortcut to Safari, like the Finder’s ⌘↑. (I could have used ⌘↑ here too, but that would have interfered with Safari’s built-in shortcut for scrolling to the top of the page. I felt that ⌘⌥↑ was the next best option.)