Firefox Multi-Account Containers might be the most useful extension that ships from Mozilla themselves. After two years of daily use, here's what it actually enables and how to set it up properly.
What Containers Actually Do
Containers create isolated storage spaces within Firefox. Each container has its own:
- Cookies and local storage
- Cache
- IndexedDB
- Session history (for pages that check referrer)
What they don't isolate: your IP address, browser fingerprint, or downloads. Containers are about session isolation, not anonymity.
The Core Use Cases
Multiple accounts on the same site: Log into two different Gmail accounts, two different GitHub accounts, or two different Slack workspaces in the same browser window. No signing out, no separate profiles.
Setup: Install Multi-Account Containers, then right-click the New Tab button → "Open New Tab in [Container]."
Work/personal separation: Create a "Work" container for all work sites. Your work Google account, work Slack, work GitHub, work email — all stay in Work. Your personal accounts stay in default.
Why this is better than two browser profiles: Profiles require switching the entire browser. Containers let you have both open simultaneously.
Banking/finance isolation: Create a "Banking" container. Your bank cookies are isolated from every other site. Cross-site tracking cookies can't follow you from your bank to a news site.
Shopping isolation: Create a "Shopping" container. Amazon doesn't see what you were browsing before you came to Amazon. This also means Amazon's advertising network can't track you on non-Amazon sites as effectively.
The Firefox Relay Integration
If you install Firefox Relay alongside containers, you can generate random email addresses for each container. Shopping gets random-alias-1@relay.firefox.com; the alias forwards to your real address but can be disabled independently.
Container Auto-Assignment
The most important feature: you can assign a site to always open in a specific container. Right-click any link or tab → "Always Open in [Container Name]."
After setup, every time you click a link to that site (from any container), it opens in the assigned container automatically. You never have to think about it.
Example setup:
-
mail.google.com(personal) → Personal container -
mail.google.com/a/yourcompany.com→ Work container -
github.com/your-work-org→ Work container -
bank.com→ Banking container
Advanced: Temporary Containers
The Temporary Containers extension (separate from Multi-Account Containers) creates a new disposable container for every new tab by default. When the tab closes, the container and all its data is deleted.
This is the maximally-paranoid setup: no persistent cookies for any site unless you explicitly assign it to a permanent container. Every browsing session is clean.
Container + VPN Combination
Some VPN providers (Mullvad, Mozilla VPN) have Firefox extensions that can route specific containers through the VPN while leaving others on your regular IP. You can have a "Privacy" container that routes through a VPN and a "Work" container that uses your regular IP for corporate access.
The New Tab Context
One minor workflow note: when you have multiple containers active, opening a new tab via the New Tab button creates it in the default container. Extensions that replace the new tab — like Weather & Clock Dashboard — run in the default container context. This is fine for a weather/clock tool that doesn't need account isolation.
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