Log in on each browser you use and one press of Fuzz or Test fuzz runs the vector in all of them, with every browser's results side by side.
This enumerates through all HTML tags and checks if the span gets HTML encoded.
Unable to render tweet button
<$[data1] id=x><span></span></$[data1]>
x.innerHTML.includes('<') && log('$[data1]')
<textarea id=x><span></span></textarea>
<title id=x><span></span></title>