various issues on puzzling.SE

From puzzling.SE.

On this question, I see the following

• the FastPreview crashes half-way through the page (TeX is still in place). The console reports MathJax.js?config=TeX-AMS_HTML-full:19 Uncaught TypeError: Cannot read property 'insertBefore' of null
• If I deactivate the Fast Preview, then I see the problem described in the post -- furthe down in the page, the rendering is all over the place and equations are duplicated. This seems to roughly match the point where the FastPreview crashes (the last answer from BigBlackBox)

I'll see if later versions of Chrome suffer from this.