Solved! I had made an elementary mistake and had a new line after the <?php ?> in my WordPress child theme functions.php. Chrome inspector did not show it to me but Firefox did: "XML or text declaration not at start of entity".
Among all the bits of the site it seems to have affected only the Simile timeline. Thanks again for a great utility, and keeping it up to date. -- You received this message because you are subscribed to the Google Groups "SIMILE Widgets" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/simile-widgets. For more options, visit https://groups.google.com/d/optout.
