OK, it runs, but I still get the following:

Code:
** (thunderbird:26380): WARNING **: Invalid borders specified for theme pixmap:
        /usr/share/themes/Lubuntu-default/gtk-2.0/images/null.png,
borders don't fit within the image

** (thunderbird:26380): WARNING **: Invalid borders specified for theme pixmap:
        /usr/share/themes/Lubuntu-default/gtk-2.0/images/scrollbar_vertical.png,
borders don't fit within the image