Use case: A screen reader providing navigation by element type (e.g. heading). Steps to reproduce: 1. Launch the attached accessible-event listener in a terminal. 2. Load the attached test case in Firefox. Expected results*: Of the three headings in the document, only one non-hidden heading would be found. Actual results: Two non-hidden headings are found because the second hidden heading has inherited this attribute from an ancestor in the tree. Output: 2 non-hidden headings found: 0. This heading is not hidden 1. This heading is hidden due to ancestry Need to check the ancestry to be sure.... -> document frame -> This heading is not hidden -> This heading is a hidden element (HIDDEN) -> section (HIDDEN) -> section -> section -> section -> This heading is hidden due to ancestry Impact: Screen readers are expected to not present elements -- and their descendants -- which are "hidden" via ARIA. If an element which inherits this attribute does not expose the fact that it is supposed to be hidden, the screen reader has to ascend the accessible tree "just in case." * N.B. This is a spin-off of bug 972845. The real expected result is that the tree would be pruned to not include the hidden elements as shown below. But unless and until that bug is resolved, Gecko should at least minimize the work ATs need to do to prune the tree themselves. Comparative output from Epiphany/WebKitGtk: 1 non-hidden headings found: 0. This heading is not hidden Need to check the ancestry to be sure.... -> document web -> This heading is not hidden