Fix stalling countdown on Linux

[burdenc]

When you mouse over a notification on Ubuntu, the countdown will stop. However, upon mousing out of the notification the countdown does not resume.

[burdenc]

This is an issue with how the notification window is created on Linux. For some reason onmouseout isn't being called when the alert is in the chromeless window. For reference, it works perfectly if you point your browser to "chrome://global/content/alerts/alert.xul". I will submit to bugzilla soon, and possibly find an (inefficient?) workaround with onmousemove.

[burdenc]

This is caused because on Linux the mouseover and mouseout events fire very rapidly and seemingly randomly when moving the mouse. This causes the mouseover event to end up running right after the mouseout event when that should not happen.