Researching bug 181921 and bug 155521 lead me to a strange conclusion: HTMLTitleElement is noncence, it could not be use it Mozilla. Testcase show, that this element not supported id, lang and dir (in contrary with HTML 4.01 standart), and bug 181921 show, that document.title does not depend on this element. As I think, source of such behaviour, is that change of document.title not linked to document.getElementByTag("TITLE").item(0), even more, function nsDocument::SetTitle(const nsAString& aTitle) does not fire change of Tittle text (in other direction fic for bug 1415 work, so if I change document.getElementByTag("TITLE").item(0).text document.title changed). I do a small overview of other title bugs, and found that bug 33878 marked fixed, although no dir, lang or id propereties of <title> is supported.

Oh, also it cover bug 118704. And, if document have no title tag his title could not be changed -- this is because if (!title.IsEmpty()) (in nsDocument::SetHeaderData function) have no else. So empty titled document could not obtain title with document.title="something"

*** This bug has been marked as a duplicate of 118704 ***