Standards support

Other criticisms, mostly coming from technically proficient users and developers of websites and browser-based software applications, concern Internet Explorer's support of open standards, because the browser often uses proprietary extensions to achieve similar functionality.

Internet Explorer supports, to some degree, a number of standardized technologies, but has numerous implementation gaps and conformance failures—some minor, some not—that have led to criticism from an increasing number of developers. The increase is attributable, in large part, to the fact that competing browsers that offer relatively thorough, standards-compliant implementations are becoming more widely used.

Internet Explorer's ubiquity, in spite of its inferiority in this area, frustrates developers who want to write standards-compliant, cross-browser code and the advanced functionality it provides, because they are often stuck coding pages around Internet Explorer's bugs, proprietary featureset, and missing standards support instead.

Web developers must work with the least advanced technology across all browsers they wish to support, and Internet Explorer is often criticized for being technically obsolete. These include supporting fewer CSS, HTML, and DOM features than Firefox or Opera and not having native XHTML support. For another long-standing concrete example, see Internet Explorer's poor PNG transparency support, which remained unfixed until Internet Explorer 7