The long-awaited page zoom feature has finally been implemented. The latest Firefox 3 nightly build now supports full-page zooming like Opera and Internet Explorer 7. Although the page zoom feature is fully implemented, the user interface doesn't expose the page zoom functionality to the end user yet. Until menu items, toolbar buttons, or keyboard shortcuts are added to facilitate access to the page zoom feature, most users probably won't be able to make much use of the new feature.

In order to test it ourselves with the latest nightly build, we poked around and figured out the underlying API so that we could alter the page zoom level with Javascript. Manipulating the page zoom requires high security access, so you can't do it directly in a web page or with a JavaScript bookmarklet. You could potentially implement support controlling page zoom by making a custom Firefox plugin, but for simple testing purposes you can also just use Firefox's built-in JavaScript error console. Launch the Javascript console by selecting Error Console from Firefox's Tools menu. Then, type the following into the code text box and click the Evaluate button:

Components.classes["@mozilla.org/appshell/window-mediator;1"].getService(Components.interfaces.nsIWindowMediator).getMostRecentWindow("navigator:browser").getBrowser().mCurrentBrowser.markupDocumentViewer.fullZoom = 3;

That will zoom in the current page to three times its normal size. You can experiment with various values to see the page at different zoom levels. If you want to zoom out, use decimals like 0.2 or 0.6. This very useful feature is yet another example of Firefox 3 improvements made possible by the excellent work that has gone into Gecko 1.9.