Tony, the second article triggers a really fascinating bug. Check out the following snippet of HTML from your page:
<a href='https://toc.oreilly.com/tag/3ms-cloud-library' title='3M's Cloud Library Tag' rel='tag'>3M's Cloud Library</a>
You will notice that the title attribute contains a single quote that is not properly escaped! I am willing to bet that you are using a plugin where someone forgot to use esc_attr. The problem is that later in the popup, JavaScript loops through the attributes of this element, and one of them ends up being tag'
, an illegal name. So, we end up with something like this getting executed:
var fragment = "<a href='https://toc.oreilly.com/tag/3ms-cloud-library' title='3M's Cloud Library Tag' rel='tag'>3M's Cloud Library</a>";
jQuery(fragment).removeAttr("tag'");
Either jQuery or the browser cannot make sense of an attribute name containing the single quote, and an InvalidCharacterError is thrown that the popup never catches. I would recommend finding the other WordPress plugin that is generating invalid HTML. To stop this error in the short term, add .entry-utility
to your exclusion list in the Send to Kindle advanced settings to stop the invalid markup from getting to the popup in the first place