This is an issue from accessible/tests/mochitest/bounds/test_zoom.html. <area> element usually has its primary frame being the corresponding <img> element. However, in Stylo, after zooming (presumably triggering reflow or reframe?), <area> element loses its primary frame. In the test specifically, the absence of primary pointer causes Accessible::Bounds to return all zeros for bounds of the element. This may have more impact than accessibility given the absent of primary frame pointer, I suppose.

I'm 99% sure this is fixed by the patches from bug 1380133.

Does the test pass with those patches?

(That bug was backed out, so I'll wait to test since I'm about to leave for today)

The test accessible/tests/mochitest/scroll/test_zoom.html doesn't seem in-tree? But the other two test_zoom.html tests pass with stylo enabled now.