When running `mach test browser/components/uitour/test/`, I get the following failures: > 1537 INFO TEST-START | browser/components/uitour/test/browser_trackingProtection.js > 1538 INFO Entering test bound setup_test > 1539 INFO Leaving test bound setup_test > 1540 INFO Entering test bound test_benignPage > 1541 INFO Load a test page not containing tracking elements > 1542 INFO TEST-PASS | browser/components/uitour/test/browser_trackingProtection.js | Info panel didn't appear on a benign page - > 1543 INFO Leaving test bound test_benignPage > 1544 INFO Entering test bound test_trackingPages > 1545 INFO Load a test page containing tracking elements > 1546 INFO TEST-UNEXPECTED-FAIL | browser/components/uitour/test/browser_trackingProtection.js | Timeout waiting for popup at anchor: Intro panel should appear - > Stack trace: > chrome://mochitests/content/browser/browser/components/uitour/test/head.js:waitForCondition/<:38 > resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:Handler.prototype.process:940 > resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:this.PromiseWalker.walkerLoop:816 > TEST-INFO | started process screenshot > Failed to start c:\fx\objdir-frontend\dist\bin\screenshot.exe for screenshot: The system cannot find the file specified > 1547 INFO TEST-UNEXPECTED-FAIL | browser/components/uitour/test/browser_trackingProtection.js | Test timed out - > MEMORY STAT | vsize 710MB | vsizeMaxContiguous 1806MB | residentFast 260MB | heapAllocated 68MB > 1548 INFO TEST-OK | browser/components/uitour/test/browser_trackingProtection.js | took 45184ms > 1549 INFO TEST-UNEXPECTED-FAIL | browser/components/uitour/test/browser_trackingProtection.js | Found a tab after previous test timed out: http://tracking.example.org/browser/browser/base/content/test/general/trackingPage.html -

Updated STR (quicker with artifact build): mach clobber hg pull -u mach build mach test browser/components/uitour/test/ This only fails if you don't run `mach test browser/base/content/test/general` before the uitour suite. Once you run the general suite, benignPage.html and trackingPage.html will exist.