If you want this fixed immediately, you can try downloading the file and replace the file SAGE_ROOT/devel/sagenb/sagenb/data/sage/js/notebook_lib.js with the downloaded file.
If you want this fixed immediately, you can try downloading the file and replace the file SAGE_ROOT/devel/sagenb/sagenb/data/sage/js/notebook_lib.js with the downloaded file.