If the tip is the last result in the popup (e.g. the only result), you key down to select the tip's main button, and then key down again to select the help button, both the help button and the first one-off become selected. I haven't tried to debug it, but it looks like the problem is that we pass in this.view.visibleRowCount here: https://searchfox.org/mozilla-central/rev/1d0e84d2ec2843924bc6e5ed6658f93439e12351/browser/components/urlbar/UrlbarController.jsm#287

The one-offs use that to determine when the selection moves from the last result to the one-offs. visibleRowCount is one less than the actual number of selectable elements, so the one-offs think they become selected one selectable element too early.

We should update the tip test for this.

Changing the summary to more accurately reflect the problem.

The one-offs compare view.visibleRowCount to view.selectedRowIndex, so not only do we need a view.visibleElementCount, we also need a view.selectedElementIndex.

https://hg.mozilla.org/mozilla-central/rev/0a3d13728cbc