Mpris-players: multiple entires in xfce4-panel.xml for firefox, vlc

During the process of automating XFCE changes, I spotted something I didn’t expect in "~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml. For the property /“plugins/plugin-9/mpris-players”, there were hundreds of entries for firefox and vlc, 230 and 162 respectively. Plugin-9 is pulseaudio. I read the archwiki on mpris.

Can anyone shed some additional light on what is happening and how to clean it up.

They take the form of:

firefox.instance10031;firefox.instance10257;firefox.instance10451

# display  property 
xfconf-query -c xfce4-panel -lv | grep mpris-players