--- a/testing/talos/talos/tests/tabswitch/api.js
+++ b/testing/talos/talos/tests/tabswitch/api.js
@@ -150,20 +150,19 @@ function loadTPSContentScript(browser) {
 /**
  * For some <xul:tab> in a browser window, have that window switch
  * to that tab. Returns a Promise that resolves ones the tab content
  * has been presented to the user.
  */
 async function switchToTab(tab) {
   let browser = tab.linkedBrowser;
   let gBrowser = tab.ownerGlobal.gBrowser;
-  let window = tab.ownerGlobal;
 
   await loadTPSContentScript(browser);
-  let start = Math.floor(window.performance.timing.navigationStart + window.performance.now());
+  let start = Cu.now();
 
   // We need to wait for the TabSwitchDone event to make sure
   // that the async tab switcher has shut itself down.
   let switchDone = waitForTabSwitchDone(browser);
   // Set up our promise that will wait for the content to be
   // presented.
   let finishPromise = waitForContentPresented(browser);
   // Finally, do the tab switch.
@@ -203,21 +202,21 @@ function waitForTabSwitchDone(browser) {
  *
  * @returns Promise
  *        Resolves once the content has been presented. Resolves to
  *        the system time that the presentation occurred at, in
  *        milliseconds since midnight 01 January, 1970 UTC.
  */
 function waitForContentPresented(browser) {
   return new Promise((resolve) => {
-    let mm = browser.messageManager;
-    mm.addMessageListener("TPS:ContentSawPaint", function onContentPaint(msg) {
-      mm.removeMessageListener("TPS:ContentSawPaint", onContentPaint);
-      resolve(msg.data.time);
-    });
+    browser.addEventListener("MozLayerTreeReady", function onLayersReady(event) {
+      let now = Cu.now();
+      TalosParentProfiler.mark("MozLayerTreeReady seen by tps");
+      resolve(now);
+    }, { once: true });
   });
 }
 
 /**
  * Given some browser, do a garbage collect in the parent, and then
  * a garbage collection in the content process that the browser is
  * running in.
  *