XUL/Firefox Extension: Determine scroll position of main window

Question

I'm developing firefox sidebar that interacts with the main browser window. When a button within the sidebar is clicked, I need to be able to determine how far down the current page the user has scrolled.

Anybody have any ideas? I can't seem to find the right combination.

Answer 1

I think the scrollTop and scrollHeight attributes should help you. You can combine it with the clientHeight attribute.

Pseudo code :

scrollPercent = 100
if(clientHeight <= scrollHeight) {
    scrollPercent = (scrollTop / (scrollHeight - clientHeight)) * 100
}

Answer 2

Found the answer for anyone else that may be looking for it:

window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
  .getInterface(Components.interfaces.nsIWebNavigation)
  .QueryInterface(Components.interfaces.nsIDocShellTreeItem)
  .rootTreeItem.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
  .getInterface(Components.interfaces.nsIDOMWindow)
  .gBrowser.selectedBrowser.contentWindow.scrollY