MathML is an XML-based standard for representing mathematical expressions in machine to machine communications which allows websites to display mathematical symbols and equations. Unfortunately, support for MathML is still lacking in many browsers. For those browsers with support, extra fonts will need to be installed.
To test whether your browser is capable of rendering MathML you can either visit some of the pages on this site or one of the MathML demos hosted by Mozilla. In particular, there is the Mozilla MathML Start Page which also contains a screenshot of what you might be missing. For the more adventurous, there is a MathML Torture Test.
To properly view pages containing MathML you will need a unicode font complete with all of the required mathematical symbols. The STIX Fonts Project has developed a comprehensive set of fonts specifically designed for mathematical material. Although the final version has not been released yet, the beta version is available to install:
The MozEX extension lets you use your own text editor to edit textareas. It’s especially useful for editing Wiki pages.
See the instructions on the Instiki website.
Install the MathPlayer plugin
Sadly Konqueror, the browser for KDE, currently does not support MathML. If you are interested in this feature, please vote for it here: Bug 30526: MathML support for Konqi.