openAboutDebugging helper: https://searchfox.org/mozilla-central/rev/eef79962ba73f7759fd74da658f6e5ceae0fc730/devtools/client/aboutdebugging-new/test/browser/head.js#27-43 only waits for a couple of DOM elements to be created before resolving. But ideally, it should wait for full initialization before resolving. Otherwise, you would get failures like I got in bug 1485661, where RDP requests being made during initialization are still pending on test end. Or you may have unexpected behavior as initialization is still processing while your test script executes. There is a couple of ways to better wait for full initialization. * From AboutDebugging.init, we could "await" for all the dispatches actions, like these two: https://searchfox.org/mozilla-central/rev/eef79962ba73f7759fd74da658f6e5ceae0fc730/devtools/client/aboutdebugging-new/aboutdebugging.js#62-63 And have the test helper somehow wait for AboutDebugging.init resolution. * We could use the existing "waitUntilState" helper, and explicitely wait for a couple of expected states from openAboutDebugging function. * There propably is some other options...

MozReview-Commit-ID: 9ClZ2lkdq01 Depends on D8868

Green try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=e2c1b64236116578b5072cb9c5cb40c0c510f89a

Green try for the latest version: https://hg.mozilla.org/try/rev/9e63cb4e5fefa1d606cc68d2705456e74d5f7d95

Pushed by apoirot@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/e732689cf7e7 Ensure that new about:debugging tests wait for initial load requests before proceeding with the tests. r=jdescottes