"Limit to designated sites" conflict with other Container addons

[erosman]

If "Firefox Multi-Account Containers" is installed and "Limit to designated sites" is enabled (without any sites listed, there will be a conflict with another container addon (FoxyTab).

I am not sure where the exact conflict is as the addons behaviours are not the same. I look forward to feedback and will work on eliminating the issue.

• FoxyTab only deals with Tab URL and although it does have "Limit to designated sites", it only comes to effect when navigating
• "Limit to designated sites" in Firefox Multi-Account Containers appears to affect the content of the tab

Actual behavior

• Default Firefox Multi-Account Containers with no sites and "Limit to designated sites" enabled
• FoxyTab set to open example.com in Personal container & "Limit to designated sites" disabled
• Opening example.com
• FoxyTab opens example.com in a new Personal container (its function ends there)
• An endless loop starts as it appears that "Firefox Multi-Account Containers" is re-navigating the tab
• No conflict occurs if "Limit to designated sites" is disabled in Firefox Multi-Account Containers

Expected behavior

Once a tab is opened in a container, there shouldn't be a need for re-navigating it

Notes

Maybe there is a need to limit access when there are more than one addon is handling an API, similar to Network Settings addons :thinking:

[erosman]

It appears that when a container tab is opened by another process and that site is not listed, and siteIsolation is true, addon attempts to remove the tab and re-open it in the default container which creates an endless loop with the other addon.

I would suggest that siteIsolation should only come into effect:

• if there are listed sites
• if the tab is navigating from a LISTED site in a container to an UNLISTED site

https://github.com/mozilla/multi-account-containers/blob/873ba0ab09bf0ea1adc555e6020a65a4c41c71bb/src/js/background/assignManager.js#L254-L272