On Windows, you should be able to get into the MathJax contextual menu by right click on any (correctly rendered) formula. This menu contains various items, you can go to Math Settings -> Math Renderer and then choose one of the renderers.
Here is a formula which you can use for testing: $$x^2+y^2=z^2.$$
Screenshot showing the MathJax menu:
On macOS (tested with Safari) it is the same, only that you get into the context menu with a “secondary click” – Control click or one of the (configurable) alternatives.
Same on a Mac. Actually, it probably depends on the browser, not on the OS. Here is Safari in MacOS.