If the page URL includes a hash reference (a link to a particular location within the page), MathJax v2.0 will jump to that location after the page has finished typsetting.  (Since the size of the page may have changed due to the mathematical typsetting, that location may no longer be visible on screen, so MathJax moves there when it is done with the initial typesetting.)  You can control this behavior with the positionToHash parameter in the main section of your configuration.

In addition to the HTML-CSS and Native MathML output available in v1.1, MathJax v2.0 includes an SVG-based output jax.  This should prove to be more reliable than the HTML-CSS output, as it avoids some CSS, web-font, and printing issues that the HTML-CSS output suffers from, and it currently has no browser-dependent code.  The SVG mode even works in some ebook readers (like Apple iBooks and Calibre).

• New mhchem chemistry extension (adds \ce, \cf, and \cee macros)
• New cancel extension (adds \cancel, \bcancel, and \cancelto macros)
• New extpfeil extension (adds more stretchy arrows)
• New color extension (makes \color work as a switch, as in LaTeX).  Adds \definecolor, other color models, LaTeX named colors, \colorbox, \fcolorbox, etc.
• New begingroup extension to allow macro definitions to be localized. Adds \begingroup and \endgroup for isolating macro declarations, and defines \let, \renewenvironment, \global, and \gdef.
• New enclose extension to give TeX access to <menclose> elements.  Adds \enclose{type}[attributes]{math} macro.
• New action extension to give TeX access to <maction> elements.  Adds \mathtip{math}{tip}, \texttip{math}{tip}, and\toggle{math1}{math2}...\endtoggle macros.
• New \mmToken{type}[attributes]{text} macro for producing <mo>, <mi>, <mtext>, and other token MathML elements directly.
• New \bbox[color;attributes]{math} macro to add background color, padding, borders, etc.
• New \middle macro for stretchy delimiters between \left and \right.
• New \label, \ref, and \eqref macros for numbered equations.
• Better implementation of \not so it produces proper MathML when possible.
• Better implementation of \dots that selects \ldots or \cdots depending on the context.
• Better implementation of \cases that automatically uses \text on the second entry in each row.
• Safer implementation of \require that only allows loading from extensions directory.
• Allow \newcomand to provide a default parameter.
• Allow \\ to take an optional argument that specifies additional space between lines.
• Allow \\ to be used anywhere (to force a line break), not just in arrays.
• Allow optional alignment parameter for array, aligned, and gathered environments.
  
  

• Work around for the OS X Lion STIX font problem.
• Support for STIX-1.1 fonts (detection of which version you have, and use data appropriate for that).
• New WOFF versions of the web fonts (smaller, so faster to download).
• Data for more stretchy characters in HTML-CSS output.
• Add support for Unicode planes 1 through 10 (not just the Math Alphabet block) in HTML-CSS output.
• Increased timeout for web fonts (since it was switching to image fonts too often, especially for mobile devices).
• Only switch to image fonts if the first web font fails to load (if we can access one, assume we can access them all).
• Allow <mtext> elements to use the page font rather than MathJax fonts (optionally).
• Provide better control over the font used for characters that are not in the MathJax fonts.
  
  

• The MathJax contextual menu has been reorganized to make it easier to get the source view, and to control the parameters for MathPlayer in IE.
• The MathJax contextual menu is available in mobile devices (see description above).
• Warning messages are issued if you switch renderers to one that is inappropriate for your browser.
• MathJax now starts processing the page on the DOMContentLoaded event rather than the onload event (this allows the mathematics to appear sooner).
• Native MathML output is now scaled to better match the surrounding font (like it is for HTML-CSS output).
• Better CSS styling for NativeMML output in Firefox in order to handle \cal and other fonts.
• MathML output now (optionally) includes class names to help mark special situations generated by the TeX input jax.  (This lets the MathML from the Show Source menu item better reproduce the original TeX output.)
  
  

• The default renderer for Firefox has been changed from NativeMML to HTML-CSS (in those configurations that choose between the two).  The only browser that defaults to NativeMML is now IE with MathPlayer installed.
  
  
• NativeMML will now be selected in IE9 when MathPlayer is present (since IE9 was released the same day as MathJax v1.1a, and there had been problems with IE9 beta releases, we weren’t sure if MathPlayer would work with the official release, and so did not select NativeMML by default.)
  
  
• The performance improvements in IE8 and IE9 now make it unnecessary to use a <meta> tag to force IE7 emulation mode.  In fact IE9 in IE9 standards mode now runs faster than IE9 in IE7 standards mode, and IE8 in IE8 standards mode is comparable to IE8 in IE7 standards mode.  We now recommend that you use
  
  

  <meta http-equiv="X-UA-Compatible" content="IE=edge">

  
  to obtain the highest emulation mode available in IE, which will be the fastest one for MathJax 2.0.

• The tex2jax preprocessor now balances braces when looking for the closing math delimiter.  That allows expressions like $y = x^2 \hbox{ when $x > 2$}$ to be properly parsed as a single math expression rather than two separate ones with unbalanced braces.  The old behavior can be obtained by setting balanceBraces to false in the tex2jax block of your configuration.
  
  
• The \cases macro now properly places the second column in text mode not math mode.  In the past, one needed to use \text in the second column to achieve the proper results; pages that did this will still work properly in v2.0.  Pages that took advantage of the math mode in the second column will need to be adjusted.
  
  
• The \dots macro now produces \ldots or \cdots depending on the context (in the past, \dots always produced \ldots).
  
  
• A one pixel padding has been added above and below HTML-CSS output so that math on successive lines of a paragraph won’t bump into each other.
  
  
• There is a new MathPlayer submenu of the Math Settings menu in the MathJax contextual menu that allows the user to control what events are passed on to MathPlayer.  This allows better control for those using assistive devices like screen readers.  When menu events are being passed on to MathPlayer, the MathJax menu can be obtained by ALT-clicking on a typeset expression (so the user can still access MathJax’s other features).
  
  
• In order to improve stability with IE when MathPlayer is installed, MathJax now adds the namespace and object bindings that are needed for MathPlayer at the time that Mathjax is first loaded, rather than waiting for the NativeMML output jax to be loaded.  Since this is before the configuration information has been loaded, this will happen regardless of whether the NativeMML output jax is requested.  This means that IE may ask the user to allow MathPlayer to be used, and may show the MathPlayer splash dialog even when MathPlayer is not in the end used by MathJax.  Note that this setup can only be performed if MathJax is loaded explicitly as part of the initial web page; if it is injected into the page later by adding a <script> tag to the page dynamically, then MathPlayer will be set up when the NativeMML jax is loaded as in the past.
  
  
• The MathJax typesetting is now started on DOMContentLoaded rather than at the onload event, when possible, so that means MathJax may start typesetting the page earlier than in the past.  This should speed up typesetting one pages with lots of images or side-bar content, for example.
  
  
• MathJax now attempts to determine whether the page’s onload event had already occurred, and if it has, it does not try to wait for the DOMContentLoaded or onload event before doing its initial typeset pass.  This means that it is no longer necessary to call MathJax.Hub.Startup.onload() by hand if you insert MathJax into the page dynamically (e.g., from a GreaseMonkey script).
  
  
• If the page URL includes a hash reference (a link to a particular location within the page), MathJax v2.0 will jump to that location after the page has finished typsetting.  Since the size of the page may have changed due to the mathematical typsetting, that location may no longer be visible on screen, so MathJax moves there when it is done with the initial typesetting.  You can control this behavior with the positionToHash parameter in the main section of your configuration.
  
  
• In the event that MathJax is not able to load the configuration file you have specified in the script tag that loads MathJax.js, it will no longer issue the warning message about a missing configuration.  The configuration process changed in v1.1, and that message was to help page maintainers update their configurations, but it turns out that for users with slow network connections, MathJax could time out waiting for the configuration file and would issue the warning message in that case, even though the page included the proper configuration.  That should no longer occur in MathJax v2.0.