This was discovered from bug 1101873. See comment 4 (https://bugzilla.mozilla.org/show_bug.cgi?id=1101873#c4) for details. The non-capturing listener should use AddSystemEventListener. To reproduce, undo the patch from that bug and follow the steps. We want to use the right listener here but something in toolbar.xml is preventing that. Maybe Dao, who wrote the toolbar auto-hide code has some insight.
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