As of bug 376811 mouse move events are ultimately routed properly most of the time, but the underlying bug in which popup windows still receive native mouse move events after being closed is still there. It is hard to explain how one might see this bug by using the browser, but user glitches are theoretically possible and event handling can be more efficient in some cases. Here is how one can see this bug as a developer: 1. Log the case in which a popup window gets a mouse move event and forwards it to the popup's parent window. 2. Open Firefox and get a tooltip to open over some content. 3. Move the mouse somewhere else on the content so that the tooltip closes. 4. Keep moving the mouse around without letting another tooltip open, notice from logging that events are still going to the closed tooltip and then getting routed to the parent window. This shows that while events are ultimately getting routed to the correct window, they are incorrectly getting routed through the closed popup window first (no incorrect gecko events are sent in this native re-routing unless the user moves the mouse over the place where the popup used to be). This incorrect re-routing stops as soon as the user clicks on some content.

Fixed by patch for bug 387164, which just landed on trunk.