Full page zoom

Full page zoom (or just fullZoom) is a new feature in Firefox 3.

Example (XUL:browser)

The following example demonstrates the use for the current focused browser window. This is the typical usage for a Firefox extension.

var zoom = ZoomManager.getZoomForBrowser(gBrowser.selectedBrowser);
ZoomManager.setZoomForBrowser(gBrowser.selectedBrowser, ZoomManager.MIN);

Example (XUL:iframe)

Note: This is probably out of date.

You may use the fullZoom feature for a <XUL:iframe> as well. However, because an iframe doesn't have a markupDocumentViewer property, we need to get that first:

var zoom = 1.5;
var iframe = document.getElementById("authorFrame");
var contViewer = iframe.docShell.contentViewer;
var docViewer = contViewer.QueryInterface(
docViewer.fullZoom = zoom;


  • Page zoom extension by Ted Mielczarek fullpagezoom.xpi for latest Firefox 3.0 nightlies
  • The bugzilla bug about fullZoom.
  • nsIMarkupDocumentViewer Interface documentation.