--- a/browser/extensions/pdfjs/test/browser_pdfjs_zoom.js
+++ b/browser/extensions/pdfjs/test/browser_pdfjs_zoom.js
@@ -93,17 +93,17 @@ add_task(function* test() {
         }
 
         // check that PDF is opened with internal viewer
         Assert.ok(content.document.querySelector("div#viewer"), "document content has viewer UI");
         Assert.ok("PDFJS" in content.wrappedJSObject, "window content has PDFJS object");
 
         let initialWidth, previousWidth;
         initialWidth = previousWidth =
-          parseInt(content.document.querySelector("div#pageContainer1").style.width);
+          parseInt(content.document.querySelector('div.page[data-page-number="1"]').style.width);
 
         for (let test of TESTS) {
           // We zoom using an UI element
           var ev;
           if (test.action.selector) {
             // Get the element and trigger the action for changing the zoom
             var el = document.querySelector(test.action.selector);
             Assert.ok(el, "Element '" + test.action.selector + "' has been found");
@@ -128,17 +128,17 @@ add_task(function* test() {
           el.dispatchEvent(ev);
           yield waitForRender();
 
           var pageZoomScale = content.document.querySelector('select#scaleSelect');
 
           // The zoom value displayed in the zoom select
           var zoomValue = pageZoomScale.options[pageZoomScale.selectedIndex].innerHTML;
 
-          let pageContainer = content.document.querySelector('div#pageContainer1');
+          let pageContainer = content.document.querySelector('div.page[data-page-number="1"]');
           let actualWidth = parseInt(pageContainer.style.width);
 
           // the actual zoom of the PDF document
           let computedZoomValue = parseInt(((actualWidth/initialWidth).toFixed(2))*100) + "%";
           Assert.equal(computedZoomValue, zoomValue, "Content has correct zoom");
 
           // Check that document zooms in the expected way (in/out)
           let zoom = (actualWidth - previousWidth) * test.expectedZoom;