It doesn't work in ncatlab.org.

[linuxmetel]

This addon doesn't work in ncatlab.org. In https://ncatlab.org/nlab/show/HomePage, I got following error message from Console tab in Firefox DevTools when I placed the cursor over a word.

XML Parsing Error: not well-formed
Location: 
Line Number 5, Column 107:

SyntaxError: An invalid or illegal string was specified