"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 🤔

[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

multi-account-containers/src/js/background/assignManager.js

Lines 254 to 272 in 873ba0a

	// - the current tab's container is locked and only allows "www.google.com"
	// - the incoming request is for "www.amazon.com", which has no specific container assignment
	// - in this case, we must re-open "www.amazon.com" in a new tab in the default container
	const siteIsolatedReloadInDefault =
	await this._maybeSiteIsolatedReloadInDefault(siteSettings, tab);
	if (!siteIsolatedReloadInDefault) {
	if (!siteSettings
	|| userContextId === siteSettings.userContextId
	|| this.storageArea.isExempted(options.url, tab.id)) {
	return {};
	}
	}
	const replaceTabEnabled = await this.storageArea.getReplaceTabEnabled();
	const removeTab = backgroundLogic.NEW_TAB_PAGES.has(tab.url)
	|| (messageHandler.lastCreatedTab
	&& messageHandler.lastCreatedTab.id === tab.id)
	|| replaceTabEnabled;
	const openTabId = removeTab ? tab.openerTabId : tab.id;