Mozilla Firefox has features that allow it to be distinguished from other web browsers, such as Chrome and Internet Explorer. Major differences To avoid interface bloat, ship a relatively smaller core customizable to meet individual users' needs, and allow for corporate or institutional extensions to meet their varying policies, Firefox relies on a robust extension system to allow users to modify the browser according to their requirements instead of providing all features in the standard distribution. While Opera and Google Chrome do the same, extensions for these are fewer in number as of late 2013. Internet Explorer also has an extension system but it is less widely supported than that of others. Developers supporting multiple browsers almost always support Firefox, and in many instances exclusively. As Opera has a policy of deliberately including more features in the core as they prove useful, the market for extensions is relatively unstable but also there is less need for them. The sheer number of extensions is not a good guide to the capabilities of a browser. Protocol support and the difficulty of adding new link type protocols also vary widely across not only these browsers but across versions of these browsers. Opera has historically been most robust and consistent about supporting cutting-edge protocols such as robust file sharing eDonkey links or bitcoin transactions. These can be difficult to support in Firefox without relying on unknown small developers, which defeats the privacy purpose of these protocols. Instructions for supporting new link protocols vary widely across operating systems and Firefox versions, and are generally not implementable by end users who lack systems administration comfort and the ability to follow exact detailed instructions to type in strings. Web technologies support Firefox supports most basic Web standards including HTML, XML, XHTML, CSS (with extensions), JavaScript, DOM, MathML, SVG, XSLT and XPath. Firefox's standards support and growing popularity have been credited as one reason Internet Explorer 7 was to be released with improved standards support. Since Web standards are often in contradiction with Internet Explorer's behavior, Firefox, like other browsers, has a quirks mode. This mode attempts to mimic Internet Explorer's quirks modes, which equates to using obsolete rendering standards dating back to Internet Explorer 5, or alternately newer peculiarities introduced in IE 6 or 7. However, it is not completely compatible. Because of the differing rendering, PC World notes that a minority of pages do not work