- Either MaC would have to hide facebook container or it would have to be able to customise it
- To enable Facebook container to have the ability to create this icon, then it would need to be exposed as part of the contextualIdentities icon list
- The about:preferences#containers list will also need to be updated to be able to customise this icon also otherwise the UI will be broken there too
TL;DR without special work to make this a hidden icon, it would be easier just to expose it to all the things and fix MaC, FB container and Firefox too.
This bug specifically will be related to adding the new icon named "fence" to the existing list within firefox.
We then have the rollout issue of enabling this with fb container to solve whilst this rides the trains. For example creating/updating a contextualIdentity with unknown icons is a rejected promise: https://searchfox.org/mozilla-central/rev/3e0f1d95fcf8832413457e3bec802113bdd1f8e8/toolkit/components/extensions/parent/ext-contextualIdentities.js#52 so the fb-container add-on will need to:
- try creating with the fence
- fallback to a circle
- then inject an override through privileged signing to fix the relevant icons
If this patch is small enough we should try and get this uplifted as far as possible to simplify the process fb container has to do here.