Rather than parse MathML directly (like Firefox and MathPlayer), Opera’s developers elected to render MathML primarily through their CSS parsing engine. Opera implements the W3C’s MathML for CSS profile. This standard defines a subset of presentation MathML 3.0 that is amenable to implementation through a CSS stylesheet. In fact, Opera developer George Chavchanidze is one of the principal arbiters of this standard.
This approach results in a pretty good rendering of most pages containing mathematical content. Even when the rendering is less than perfect, you can generally make out the intent of the author when reading mathematics with Opera. However, to date, there are readily observable problems with this approach.
CSS-based MathML rendering support was introduced in Opera 9.5.
As previously discussed, the quality of Opera’s math rendering depends in large degree upon the fonts available to Opera. If you want a decent math browsing experience with Opera:
Use a modern version of Windows (Vista, Windows 7, or Windows 8). Microsoft’s Cambria font family is native to these operating systems. The Windows Opera users can view MathML quite nicely when the Cambria fonts are available.
For Windows XP, make sure either the Cambria Math font or the STIX fonts are installed on your system.
Use a modern version of OS X. Apple has packaged the STIX fonts with all OS X releases since OS X 10.7 (Lion). For older versions of OS X, Apple’s native Apple Symbols font provides support for many Greek and mathematical characters. Mac OS X 10.5+ Firefox users can view MathML reasonably well without supplemental font support.
Use a modern Linux distribution. Most Linux distributions provide good coverage of math and Greek symbols in a variety of preinstalled unicode fonts. Linux Opera users can view MathML quite well without supplemental font support.
For more information, see the discussion of math fonts in Section 7 of this document.