User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:17.0) Gecko/20100101 Firefox/17.0 Build ID: 20121129165506 Steps to reproduce: Loaded an XML document which is transformed to HTML in Firefox via the "xml-stylesheet" processing instruction. For example this page: http://www.w3schools.com/xsl/cdcatalog_with_xsl.xml Then opened the "Web Console" in Firefox and executed this line of JS: window.performance === null Actual results: This returned 'true': window.performance === null Meaning that window.performance is null and therefore not available and any code which expects to use it will throw exceptions. Expected results: This should return 'false': window.performance === null window.performance should be available regardless of how the page is generated, like it is in every other that provides support for Navigation Timing.

Duplicate of bug 804069?

Yes.