mozilla/multi-account-containers#1617 (comment) began:
In my case with a Control-Click …
mozilla/multi-account-containers#1617 (comment) mentioned Facebook and Google.
- Use about:profiles in Firefox
88
to create then launch a profile named 1617 - add Firefox Multi-Account Containers
7.3.0
- click the toolbar button to begin the tour
- decline the invitation to synchronise
- add a Facebook container
- open https://en-gb.facebook.com/ in a new tab
- use the address bar menu to always open
en-gb.facebook.com
in the Facebook container - close the contained Facebook tab
- close the non-contained Facebook tab
- open https://en-gb.facebook.com/ in a new tab
- the always decision was not respected
- ☑ Remember my decision for this site
- Open in Facebook Container
- close the tab
- add a Google container
- open https://www.google.co.uk/ in a new tab
- use the address bar menu to always open
www.google.co.uk
in the Google container - close the contained Google tab
- close the non-contained Google tab
- open https://www.google.co.uk/ in a new tab
- the always decision was not respected
- ☑ Remember my decision for this site
- Open in Google Container
- I agree
- seek Facebook
- Control-Click the uppermost search result
- observe https://en-gb.facebook.com/ in the one new tab
– no duplication.