Best regards.
Christophe
There is a plugin for Mozilla-based browsers (including Firefox) to add SVG
support to them.
Outside of this there is very little support for MathML. However, the LaTeX
printer + jsMath works well in many situations. Furthermore there is a package
called Lasym that can render MathML.
Regards, Freddie.
For testing I remember using GtkHTML: http://en.wikipedia.org/wiki/GtkHTML
Just remember sometimes you have to translate Content MathML (which
sympy produces) to Presentation MathML. I think there is a tool to do
this somewhere in sympy/utils/mathml