I was wondering why in some comments there are white gaps (or blank spaces)?
My browser is Firefox version 43.0.4 (Ubuntu OS).
For example from question Show that $d(x,y)$ in a metric on $X$. I get the following display:
According to comments, the easiest solution is switching the Math Renderer via
MathJax menu > Math Settings > Math Renderer > Common HTML
To get the MathJax menu, right-click any formula (Control-click on a Mac).
The Common HTML renderer appears to be the future focus of MathJax, so we may as well use more of it and report any issues with that renderer.