Comment 1 for bug 1001902

In fact, none of the xdg-utils scripts work with Mate. Generally they should treat Mate as GNOME, but they fail to recognise it.
There's a detectDE function which checks for GNOME...
    elif [ x"$GNOME_DESKTOP_SESSION_ID" != x"" ]; then DE=gnome;
but is should also check for Mate ...
    elif [ x"$MATE_DESKTOP_SESSION_ID" != x"" ]; then DE=gnome;
That will make the xdg-utils treat Mate as GNOME.

To be more rigorous, use
    elif [ x"$MATE_DESKTOP_SESSION_ID" != x"" ]; then DE=mate;
That allows xgd-utils scripts to contain functions for Mate separately.

These scripts contain detectDE
xdg-desktop-icon, xdg-desktop-menu, xdg-email, xdg-icon-resource, xdg-mime, xdg-open, xdg-screensaver, xdg-settings
but only
xdg-email, xdg-mime, xdg-open, xdg-screensaver and xdg-settings use it to determine which routines to call.

This bug is pretty fundamental to Mint. For example, mintwelcome uses xdg-open to call the browser to display its
links. If xdg-open doesn't work properly, mintwelcome launches chrome but won't close and stays in focus hiding the
help page you've just launched. With amended xdg-utils, mintwelcome launces firefox or chrome as appropriate and
"Close" works properly.

I'm attaching patches which seem to work. But I'm not sure that I've understood what xdg-screensaver is supposed todo and xdg-settings just uses the GNOME functions.