I found this example of mathjax code that overflows when rendered:
$\color{red}{\textrm{Bacon ipsum dolor amet spare ribs shank cupim salami shoulder meatball sirloin chislic kevin swine cow meatloaf landjaeger filet mignon prosciutto. Hamburger cow salami ham jerky bresaola shankle porchetta sausage shoulder. Short ribs tail fatback porchetta pastrami brisket pork chop, doner rump sausage. Cupim swine flank porchetta rump. Biltong jowl corned beef kevin.}}$ I believe it is the \textrm command that causes it, as removing it makes the text obey the constraints.
I also think this issue is present on all sites that have mathjax rendering enabled - Physics, and Math, among others. Ironically, not the TeX site.
This is what it looks like in the preview:
The same issue is present after you post, as well. I initially saw the issue in a posted answer:

