_sendMediaTelemetry now runs from an idle callback started off _scheduleArbitrarilyLateIdleTasks, and can run at a time when there's no browser window, which means RecentWindow.getMostRecentBrowserWindow() can return null.

Comment on attachment 8905242 [details] Bug 1397232 - Use the hidden window to report media telemetry. I discussed this with Felipe yesterday over IRC. I don't think silencing the error and silently failing to collect telemetry data is a good idea. From our discussion, it seems the best path forward is to avoid using RecentWindow.jsm, and instead use the hidden window.

Comment on attachment 8905242 [details] Bug 1397232 - Use the hidden window to report media telemetry. https://reviewboard.mozilla.org/r/177032/#review182474 ::: browser/components/nsBrowserGlue.js:952 (Diff revision 2) > this._firstWindowLoaded(); > }, > > _sendMediaTelemetry() { > - let win = RecentWindow.getMostRecentBrowserWindow(); > + let win = Services.appShell.hiddenDOMWindow; > + if (win) { I don't think we need this null check when using the hidden window. I guess it's a leftover from the previous version of the patch.

Comment on attachment 8905242 [details] Bug 1397232 - Use the hidden window to report media telemetry. https://reviewboard.mozilla.org/r/177032/#review182890 LGTM

Pushed by felipc@gmail.com: https://hg.mozilla.org/integration/autoland/rev/4f3ba0330ce0 Use the hidden window to report media telemetry. r=florian