D3E spec defines "HistoryBack" and "HistoryForward" keys. However, IE9 users "BrowserBack" and "BrowserForward". And there are some "Browser" prefixed key names for the keys to navigate browsing. So, I think that for both compatibility with IE9 and other key names, they should be "BrowserBack" and "BrowserForward".
Fixed in the latest version of the spec: r240