If Marionette hasn't been enabled we shouldn't run any of its code. Right now this happens because the component registers the profile-after-change observer notification. And as such we register for various other notifications, and in the worst case quit Firefox if eg. a XML parse error happens. See bug 1616856 for details.

I would suggest that we read the value of the marionette.enabled pref only during startup, and never update it when a user changes the pref during runtime. That way we can safely skip all the observer registrations, and don't have to worry about inconsistent states.

Depends on D67035

Depends on D67036

https://treeherder.mozilla.org/#/jobs?repo=try&revision=bc0a548be86d640d15ddfbf90b1bf6058d9de6cf

https://hg.mozilla.org/mozilla-central/rev/0656956fe08b
https://hg.mozilla.org/mozilla-central/rev/5d11cda6e6ad
https://hg.mozilla.org/mozilla-central/rev/cd3e1f0bdeeb

The patch landed in nightly and beta is affected.
:whimboo, is this bug important enough to require an uplift?
If not please set status_beta to wontfix.

For more information, please visit auto_nag documentation.

Thanks for the reminder. We should indeed uplift this test-patch to beta.

Could we safely uplift this to 75?

(In reply to Henrik Skupin (:whimboo) [⌚️UTC+1] from comment #8)

Thanks for the reminder. We should indeed uplift this test-patch to beta.

Ah, commented before I saw this - I think you normally need to request beta approval if you want uplift?

Yes you are right. Just clarified with RyanVM on Matrix.

I just went through all the options for enabling Marionette, and I can verify with a Nightly build that only with those set Marionette will run.

Comment on attachment 9133671 [details]
Bug 1622012 - [marionette] Only initialize Marionette during startup if explicitely enabled.

Beta/Release Uplift Approval Request

• User impact if declined: Marionette registers some observer notifications during startup even when it hasn't been enabled. As result it will force close Firefox in case of XML parsing errors.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Disabling the registration of observer notifications won't cause Marionette to get partially initialized.
• String changes made/needed: None

Comment on attachment 9133671 [details]
Bug 1622012 - [marionette] Only initialize Marionette during startup if explicitely enabled.

approved for 75.0b10

https://hg.mozilla.org/releases/mozilla-beta/rev/4dbdf745dd8c
https://hg.mozilla.org/releases/mozilla-beta/rev/847777a9208c
https://hg.mozilla.org/releases/mozilla-beta/rev/acafefc48432