taffybar is unable to find the urxvt icon unless I
happen to start taffybar in /usr/share/pixmaps.

I believe this is because rxvt-unicode.desktop
specifies the icon file as neither a name that
can be found in a GTK theme directory nor an
absolute path.

This is based on a reading of the .desktop spec[0]
and inspection of all the other files in
/usr/share/applications .

[0] https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html