We actually switched in Marionette to use the `browser-idle-startup-tasks-finished` notification. Hereby we can also see delays at least for CI jobs. This is covered by bug 1794745. At least on MacOS I haven't seen a delay of such type anymore for quite some time. So I would propose to close this bug as WFM. I'll reopen in case I have some reproducible testcase or a recorded profile from such a delay during startup.
Bug 1648224 Comment 23 Edit History
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We actually switched in Marionette to use the `final-ui-startup` notification. Hereby we can also see delays at least for CI jobs. This is covered by bug 1794745. At least on MacOS I haven't seen a delay of such type anymore for quite some time. So I would propose to close this bug as WFM. I'll reopen in case I have some reproducible testcase or a recorded profile from such a delay during startup.