This is reproduced on Math SE and Electronics SE. I assume it is reproduced on all Mathjax-enabled sites.
Currently if I try to open https://electronics.stackexchange.com/questions/ask and ask a question in Firefox or Chrome the preview won't work. Here's a screenshot:
You see, there's no text in the preview area, no toolbar and there's a "Mathjax not defined" error message in the JavaScript console. Firefox console shows the same error message.
Uncaught TypeError: Object #<HTMLStyleElement> has no method 'createTextNode'