-webkit-writing-mode: vertical-lr; does not work on input text element.
but can work on contenteditable div.
Created attachment 203756 [details]
Created attachment 203757 [details]
Submitted test on various input and button elements and vertical-lr writing mode:
a) the test uses a "SHOULD": so passing that test is recommended but not required to be able to claim conformance with the spec.
b) the tests in all CSS test suites never use vendor prefixes
This issue have a relation to https://bugs.webkit.org/show_bug.cgi?id=70211
Created attachment 315962 [details]
Form controls don't go vertical
Your attachment 203757 [details] (mongolian_text_expected.PNG expected result) most likely originate from Firefox rendering... but I want to point out that the used content height of text input should not be too tall (approx. 500px in your attachment 203757 [details] screen shot, which is too much), especially since you did not specify the size attribute for that text input in your test/mongolian_text.html test. The default size in HTML5 for text input is 20 characters.