Bookmark Containers от Aleksandar Terentić

Bookmark Containers lets you pin a bookmark to a Firefox container. Set it once and forget it: the bookmark opens in that container every time, with nothing to confirm.

HOW TO USE

1. Right-click any bookmark - in the toolbar, sidebar, menu, or Library.
2. Choose "Set container" and pick one. "No container (default)" clears it again.

The container is written into the bookmark's name as a suffix, so "Gmail" becomes "Gmail [Work]". That suffix is the only thing this add-on stores. It means your setting travels with Firefox Sync to your other devices, survives uninstalling the add-on, appears in bookmark exports, and can be edited by hand in Firefox's own bookmark dialogue. Typing a container's name in the address bar finds every bookmark set to it.

Your bookmark's URL is never modified, so favicons and everything else about the bookmark behave exactly as before.

This is the missing piece next to Firefox Multi-Account Containers, which assigns whole sites to a container. Bookmark Containers works per bookmark, so two bookmarks on the same site can open in different containers - two mail accounts, two GitHub organisations, staging and production on one host.

WHAT IT NEEDS ACCESS TO

To send a bookmark into its container, the add-on has to catch the navigation before the page loads and reopen it in the right container. Nothing is ever fetched in the wrong container first. It watches only the sites you have actually set a container on, and stops watching as soon as you clear them.

No data is collected, sent anywhere, or stored outside your own bookmarks.

Requires containers to be enabled in Firefox (they are, by default).

Source code, issues, and the full list of caveats: https://github.com/aterentic/bookmark-containers

Two notes on it. The Multi-Account Containers paragraph is the one that will do the most work - it tells a reader in one line what this does that the add-on they already have doesn't. And the access section exists because <all_urls> shows up as "Access your data for all websites" on the install prompt; saying why up front prevents the uninstall that otherwise follows.