Required version: 6.0 or later (current version is 6.0 SP1)
The latest version of IE is always available from http://www.microsoft.com/ie It is well worth updating to 6.0 SP1 even if you have 5.5 or 6.0, it won't affect MathML rendering but there were several security and other patches in the SP1 release.
If you have IE 6 (but not 5.5) The mathematics will be displayed, to some extent, without any additional plugin, but to produce high quality mathematics rendering you should obtain the free MathPlayer behavior available from Design Science. The latest version is available for download from http://www.mathplayer.com/en/products/mathplayer/welcome.asp.
All versions of Mozilla (from around 0.94) should display XHTML + MathML documents by default. MathML support is part of the core rendering engine in this browser.
You may need to install additional fonts (if so, a dialog box will alert you when you first view a page containing mathematics).
A font installer has been produced at
MIT,
a local copy is here.
Instructions on the use of the installer
are
available, although it should be self explanatory.
Netscape from Version 6 onwards is based on a version of Mozilla, so the notes above apply. Don't use Version 6.x as it is very slow; Version 7.x should work without problems.
Amaya should just work out of the box, it includes support for XHTML and MathML by default. However its rendering is not up to the quality of MathPlayer or Mozilla.