One of the very best Firefox extensions, the All-in-One Sidebar add-on creates an active, collapsible sidebar that forces the default add-on window, your history, Web development tools, and what can seem like an endless amount of content to open in it.
By making all this extra content available via the same sidebar window, it takes one click on the sidebar's menu to switch among them, minimizing the clutter multiple Firefox extensions can unfortunately create. By default, the sidebar appears as a narrow panel of icons on the left of the screen, but even that can be set to automatically collapse into a thin tab that expands when moused over. It also provides a vertical toolbar to keep clutter on the main toolbar to a minimum.
Complete, well-designed, and enormously helpful, All-In-One Sidebar ranks among the most useful extensions we've seen.