LaTeX Tabular environment - mathjax/MathJax-docs GitHub Wiki
From https://groups.google.com/d/msg/mathjax-users/4btEfmThia0/GqH99mEZGLwJ
MathJax doesn't implement tabular, because it is really a text-mode environment. You can use the array environment as a replacement. E.g.
\newcommand\T{\Rule{0pt}{1em}{.3em}}
\begin{array}{|c|c|}
\hline X & P(X = i) \T \\\hline
1 \T & 1/6 \\\hline
2 \T & 1/6 \\\hline
3 \T & 1/6 \\\hline
4 \T & 1/6 \\\hline
5 \T & 1/6 \\\hline
6 \T & 1/6 \\\hline
\end{array}
should get what you are looking for.
Davide