Backed out changeset e6a9c98d62d0 (bug 927196) for causing bug 939269

browser/extensions/shumway/content/shumway.js

content/base/src/nsXMLHttpRequest.cpp

content/base/src/nsXMLHttpRequest.h

content/base/test/file_restrictedEventSource.sjs

content/base/test/mochitest.ini

content/base/test/test_XHR_parameters.html

content/base/test/test_XHR_system.html

content/base/test/test_bug338583.html

content/base/test/test_bug426308.html

content/base/test/test_bug431701.html

content/base/test/test_bug804395.html

content/base/test/test_bug927196.html

content/base/test/test_xhr_forbidden_headers.html

dom/permission/tests/test_systemXHR.html

dom/workers/XMLHttpRequest.cpp

dom/workers/test/test_xhr_system.html

dom/workers/test/test_xhr_system.js

testing/mochitest/manifest.webapp