Roger Sidje has posted a comprehensive update on the progress of MathML rendering support in Mozilla over at mozilla.org.

Sidje reports that:

Efforts of the MathML project have culminated to the point where all presentational tags are recognized ... Some presentational tags need another pass to further beautify their layout ... Also, further work remain to render <mtable> in a fully standards compliant manner

The report contains several screenshots of MathML rendered in Mozilla.

More details on the project can be found at the MathML in Mozilla page.