(into bug974736) Bug 974745 - Create click event on Sponsored Tiles to show explanation panel on mouseover (with delay)
Add XUL panel
Open panel on sponsored-button click event
Show active sponsored button on panel popup
Use more descriptive and consistent names
Use attribute to keep sponsored button state
Hide the panel if "Learn more" link is clicked
Loading new tab upon "Learn more" click, makes panel invisible wihtout invoking "popuphidden" events. Hence, explicit hidePopup() in the link's onclick handler.
Add space before { for css styling fix.
Simplify panel xul to not need hbox/vbox.
Fix panel styling/spacing of text.
Link to SUMO article for sponsored tiles.