We are trying to use the best technologies available to make the DLMF content as useful and accessible as we can. Thus, we are now using the new (almost-)standard for HTML, HTML5, as the primary format for our web content. This new format incorporates MathML as well as SVG. MathML has long been considered to be important for representing mathematics on the web; it provides for much better accessibility, reusability and scalability to different displays. Although we are not yet encoding our graphics in SVG, will be looking to make that conversion in the future.
Most modern browsers support either MathML, or the MathJax fallback acceptably; If yours does not, please consider upgrading. Also see About MathML for help for solving problems with MathML in your browser. If none of those solutions work for you, you may explicitly choose a format such as HTML+images, using images for mathematics, at Customize DLMF. Although we have attempted to follow standards and maintain backwards compatibility with older browsers, you will generally get the best results by upgrading to the latest version of your preferred browser.