AboutLoginsChild is here:

https://searchfox.org/mozilla-central/rev/b2b0077c2e6a516a76bf8077d6f0237c58f5959a/browser/components/aboutlogins/AboutLoginsChild.jsm

and here's the parent class (a singleton):

https://searchfox.org/mozilla-central/rev/b2b0077c2e6a516a76bf8077d6f0237c58f5959a/browser/components/aboutlogins/AboutLoginsParent.jsm

and here's the registration: https://searchfox.org/mozilla-central/rev/b2b0077c2e6a516a76bf8077d6f0237c58f5959a/browser/components/BrowserGlue.jsm#222-260

After the port, this code can go away: https://searchfox.org/mozilla-central/rev/b2b0077c2e6a516a76bf8077d6f0237c58f5959a/browser/components/BrowserGlue.jsm#638-654

Depending on how much work this is we may want to do bug 1558832 instead (which means doing bug 1535331 but that needs to be done anyways).

Tentatively moving all bugs whose summaries mention "Fission" (or other Fission-related keywords) but are not assigned to a Fission Milestone to the "?" triage milestone.

This will generate a lot of bugmail, so you can filter your bugmail for the following UUID and delete them en masse:

0ee3c76a-bc79-4eb2-8d12-05dc0b68e732

https://hg.mozilla.org/mozilla-central/rev/91b4e153366b