Download buffers are opened automatically whenever you start a download, and whenever you use the `download-show` command.  Those buffers can be opened in a new window, or in a new buffer in the current window.  The default for the former is to open them in a new window, and for the latter in a new buffer in the current window.  The variable `download_buffer_automatic_open_target` controls the behavior of automatically opened downloads.  Its default is `OPEN_NEW_WINDOW`.

If you don't want a download buffer to open automatically ever, put the following in your rc:

{{{
remove_hook("download_added_hook", open_download_buffer_automatically);
}}}

To open a download buffer manually, do `M-x download-show`.  You will be prompted for a download from a list of your current downloads.  By default, the download buffer will be opened as a new buffer in the current window.  With universal-argument, it will be opened in a new window.  This can be configured with the alternates system.  For example:

{{{
set_handler("download-show",
            alternates(download_show_new_window,
                       download_show_new_buffer));
}}}

Within a download buffer, the following key bindings are in effect:

|| d      || download-cancel          || Cancel the download.  File will be deleted. ||
|| p      || download-pause-or-resume || Toggle the paused state of the download. ||
|| r      || download-retry-or-resume || Resume or restart a paused or cancelled download. ||
|| delete || download-remove          || Remove the current download from the download manager. This command can only be used on inactive (paused, canceled, completed, or failed) downloads. ||
|| C-d    || download-remove          || ||
|| x      || download-shell-command   || Run a shell command on the downloaded file.  If the download is not complete, the action will be queued. ||
|| o      || download-shell-command   || ||

It comes as a surprise to many people that the `g` key, and other bindings found in content buffers are not available in download buffers.  Much of this is due to the separation of buffer types for security: a special buffer cannot become a content buffer, and a content buffer cannot become a special buffer.  It is also worth bearing in mind that single-key alphanumeric bindings are always considered context-based shortcuts in Conkeror.  To browse to an url in a new content buffer, use `C-x C-f`.

If you would rather use the Xulrunner built-in Downloads window, like Firefox has, you can open it by `M-x download-manager-show-builtin-ui`.