In Firefox, the error is that "&" is not being escaped
<title>Qt 5.12.1, Readline 8.0.0, Frameworks 5.55.0 & KDE Apps 18.12.2</title>
I suggest change the title and description lines to these
<title>'.htmlentities($m->data->attributes->title, ENT_XML1 | ENT_QUOTES,'ISO-8859-1', true).'</title>
<description>'.htmlentities(substr(preg_replace('/[^\x20-\x7E]/','', strip_tags($m->included[0]->attributes->contentHtml)), 0, 140), ENT_XML1 | ENT_QUOTES,'ISO-8859-1', true).'...</description>