Bug 1077652 - Link a preloaded <xul:browser> to a newly created tab instead of swapping docShells
[TODO] Bug 1077652 - Revert change from bug 794041 that makes test_docload.html expect accessibles in the hidden window
[TODO] Bug 1077652 - Let the test_tabbrowser.xul a11y test know about the extra preloaded document