A little known feature of Firefox-based browsers is that they let you define keywords for bookmarks. Typing such a keyword in the URL bar will then directly open the bookmark. You can use this to easily trigger Downstyler with keyboard-only input: just press ctrl+l and type whatever keyword you added to the bookmarklet. One possible downside of this approach is that it modifies the URL bar, but a quick ctrl+l, ctrl+z, ctrl+z can retrieve the previous URL if needed.