Instiki uses MathJax to render mathematics on browsers that don’t support MathML (either natively, or through a plugin). That’s slow (and, with mixed MathML/SVG content, somewhat buggy) so it’s preferable to have a browser that supports MathML and SVG natively.
In practice, that mean one of the Mozilla family of browsers. Firefox and Seamonkey work very well for rendering XHTML+MathML+SVG content. Safari (10.1 and later) is also quite good.
There’s an ongoing project to bring MathML support to Chromium. Which means that, someday, Google Chrome and Microsoft Edge will also natively support MathML.
12 Jan 2023 — MathML now supported by Chrome web browser. This week marked an incredible milestone in internet history.
The MathPlayer plugin provides MathML support for IE < 11. Apparently, it no longer works in IE 11 or later.