User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2738.0 Safari/537.36 Steps to reproduce: Load a page and wait for a variable to be set on the window object within that page using selenium-webdriver (This is from node). driver.get(url) .then(() => { // We get webdriver to wait until window.testsuite.testResults is defined. // This is set in the in browser mocha tests when the tests have finished // successfully return driver.wait(function() { return driver.executeScript('return window.testsuite;'); }); }); I've added wires to my path and telling firefox to use marionette with: const ffOptions = new firefoxOptions.Options(); ffOptions.useMarionette(true); return new webdriver .Builder() .forBrowser(this.getSeleniumBrowserId()) .setFirefoxOptions(ffOptions) .build(); Actual results: window.testsuite is always null, even when I check the console and print window.testsuite directly in the developer tools and see that it's not. Expected results: It should return the object stored in window.testsuite.

I suspect this is a duplicate of bug 1123506. Can you verify with Nightly that this is fixed?

Completely right, seems to be working on nightly - missed it due to tests stalling on a different issue with Firefox :( Thanks for following up.