The accessibility tree shows that something is a heading, but its properties do not reveal what level the heading is. You can tell by the associated node I suppose, but once we fix bug 998590 comment 6 that'll be less reliable, and it's also not a great way to get at that information.
Bug 1588784 Comment 0 Edit History
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The accessibility tree shows that something is a heading and under attributes you can find its level, but it would be nice if this was a little more prominent, perhaps even visible in the main tree given its significance. (See also bug 998590 comment 6.)