3 Internet Explorer
Long story short, Internet Explorer does not currently provide native rendering of MathML. Without supplemental support, mathematical content is often unintelligible.
However, there is a good news/bad news scenario concerning general purpose MathML browsing with Internet Explorer. The good news is a well-established plugin for IE6-IE8 called MathPlayer is provided by Design Science, Inc. It is free and you can download it from their web site.
The bad news is Internet Explorer 9 and Internet Explorer 10 break MathPlayer integration. Design Science made a “preview” release of MathPlayer 3.0 in December 2011. MathPlayer 3.0 is billed as IE9 compatible. We have had spotty luck with the product. There have been no recent updates to this “preview” release. It does not claim to be IE10 compatible.
This being the case, Internet Explorer users who require general purpose MathML support would be wise to avoid IE9 and IE10 at the current time. The situation is unfortunate since, in many respects, these browsers are an improvement over their precursors. As too often happens with Microsoft, progress in internet browsing seems to be two steps forward, one step back.