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The Mount Tray application is used to facilitate the mounting and unmounting of USB storage devices. It is included in Control Panel, meaning that in can be used within any window manager, even those that do not provide a USB mounting utility.
The Mount Tray uses the de-info script to determine the current window manager. If that window manager has a file manager, it will use it by default. If it can not find a default file manager, Mount Tray will provide an "open with" dialogue so that you can select the utility to use to browse the contents of the USB device.