/usr/share/rhythmbox/plugins/ is in rhythmbox-plugins 3.0.2-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/rhythmbox/plugins/audioscrobbler/
/usr/share/rhythmbox/plugins/audioscrobbler/Last.fm-symbolic.svg
/usr/share/rhythmbox/plugins/audioscrobbler/audioscrobbler-preferences.ui
/usr/share/rhythmbox/plugins/audioscrobbler/audioscrobbler-profile.ui
/usr/share/rhythmbox/plugins/daap/
/usr/share/rhythmbox/plugins/daap/daap-prefs.ui
/usr/share/rhythmbox/plugins/daap/daap-toolbar.ui
/usr/share/rhythmbox/plugins/daap/remote-icon.png
/usr/share/rhythmbox/plugins/fmradio/
/usr/share/rhythmbox/plugins/fmradio/fmradio-popup.ui
/usr/share/rhythmbox/plugins/fmradio/fmradio-toolbar.ui
/usr/share/rhythmbox/plugins/ipod/
/usr/share/rhythmbox/plugins/ipod/ipod-info.ui
/usr/share/rhythmbox/plugins/ipod/ipod-init.ui
/usr/share/rhythmbox/plugins/ipod/ipod-toolbar.ui
/usr/share/rhythmbox/plugins/lyrics/
/usr/share/rhythmbox/plugins/lyrics/lyrics-prefs.ui
/usr/share/rhythmbox/plugins/mtpdevice/
/usr/share/rhythmbox/plugins/mtpdevice/mtp-info.ui
/usr/share/rhythmbox/plugins/mtpdevice/mtp-toolbar.ui
/usr/share/rhythmbox/plugins/rblirc/
/usr/share/rhythmbox/plugins/rblirc/rhythmbox_lirc_default
/usr/share/rhythmbox/plugins/replaygain/
/usr/share/rhythmbox/plugins/replaygain/replaygain-prefs.ui