Several accounts, one browser, no signing out

The request sounds simple. Two Google accounts, two Slack workspaces on different email addresses, a Notion for the company and one for everything else, all open at the same time, in one browser, without signing out of anything. Every browser claims to support this. Every browser supports a slightly different version of it, and the differences only become visible on the day a shared document opens under the wrong identity in front of a client.

What follows is the mechanism behind each approach, the exact point where each one leaks, and how the services themselves change the answer. The choice is less about which browser is better and more about where the boundary between sessions gets drawn.

What one browser is actually being asked to do

Underneath the question there are two very different problems wearing the same words.

The first is being signed in to the same service twice at once. Two Gmail inboxes. Two Slack workspaces. Two Notion workspaces on separate accounts. Here the obstacle is technical: a login is a cookie scoped to a domain, and one cookie jar can only hold one signed in identity for that domain unless the service has built something specific to allow more.

The second is keeping many different services and many identities visible without losing track of which is which. Here nothing is technically broken. The obstacle is attention. Forty tabs of correctly isolated sessions is still forty tabs.

Most advice online answers the first problem and leaves the second untouched, which is why a setup can be technically perfect and still feel like a mess. Deciding which of the two is actually the daily cost is the whole decision.

The four ways a browser holds two sessions

Approach	What gets separated	What stays shared	Real cost
Service side multiple sign in	The account index inside one service	Cookies, history, extensions	External links open under the wrong account
Firefox containers	Cookies and site storage per container	Window, history, extensions, bookmarks	Only Firefox, and links need rules to route correctly
Browser profiles	Cookies, history, extensions, settings	Nothing between profiles	A window switch to change identity
Private windows	Everything, until the last one closes	Session shared across open private windows	Signing in again every time

Service side multiple sign in is what Google offers when a second account is added from the avatar menu. Both accounts stay signed in, and the account currently in view is written into the address as an index, so the first account sits at the /u/0 path and the second at /u/1. It is the fastest option and the shallowest, because the cookie jar was never divided.

Firefox Multi-Account Containers is the only mainstream feature that divides the cookie jar without dividing the window. Each container is a colour coded tab with its own storage, so two Gmail accounts can sit next to each other in the same window as genuinely separate visitors.

Profiles, available in Chrome, Edge, Brave and Vivaldi, divide everything. Two profiles are effectively two browsers that happen to share an application. The separation is complete, which is why it is the answer most security reviews accept.

Private windows look like a fifth option and are not one. All open private windows share a single session, so a second private window cannot hold a second account of the same service, and everything is discarded on close.

Where each one leaks

Multiple sign in leaks at the boundary of the browser. A link that arrives in a Slack message, a calendar invitation, or an email carries no account index, so it opens under whichever account holds the /u/0 position. On a document the reader has access to under only one identity, the result is a permission error and a manual switch. This happens dozens of times a week for anyone who receives shared links, and it is the single most common reason people abandon multiple sign in.

Containers leak at routing rather than at isolation. The isolation is correct. The problem is that a link clicked outside Firefox, or clicked in an unassigned tab, has no container assigned, so it opens in the default one. The "Always open this site in this container" rule fixes the common cases and cannot fix a domain shared by two accounts, which is exactly the situation containers were installed for.

Profiles leak at the human layer. Nothing is technically shared, and that is the point. What breaks is the reader's model of which window is which, since on macOS every profile window belongs to the same application icon in the Dock. Two identical looking windows, one work and one personal, are a mistake waiting for a screen share. Naming each profile and giving it a distinct colour and avatar reduces this considerably and is worth doing on the day the second profile is created.

The services do not behave the same way

Advice that treats every web app as equivalent falls apart quickly, because the services made different decisions.

Google supports multiple sign in and expresses it in the address bar, which works well inside Google and poorly for links arriving from elsewhere. Some Google surfaces still handle the index inconsistently, and a shared Drive link is the usual place it shows.

Slack is easier than expected. Each workspace lives on its own subdomain with its own cookie, so several workspaces stay signed in together in one browser even when the email addresses differ. The friction is notifications rather than sessions, since browser tabs do not deliver them as reliably as an installed application.

Notion takes the opposite approach. Multiple accounts can be attached to one Notion login and switched from the sidebar, which means the switching lives inside the product. Two entirely separate Notion sessions in one browser still require a container or a profile.

Microsoft 365 is the one that most often forces a decision. Signing in to a second work or school account in the same browser session commonly disturbs the first, and a profile is usually the shortest path to a stable answer.

The practical rule is to check the service before designing the setup, because a browser level fix is unnecessary for Slack and unavoidable for Microsoft.

Two smaller patterns are worth knowing because they cause the same confusion in different clothing. Some services distinguish an account from a workspace, so a single login can hold several workspaces and no browser trick is needed at all. Others treat every workspace as a separate login on the same domain, which puts the whole burden back on the cookie jar. Reading which model a service uses takes a minute and saves an afternoon of installing extensions that were never going to help. The other pattern is single sign on. When several services authenticate through one identity provider, separating those services in the browser does not separate the identity behind them, and signing out of the provider in one place can end the session everywhere. Anyone whose work accounts sit behind a company identity provider should test that behaviour before assuming the containers are holding.

Setting up a second profile so it survives the week

Most setups fail not because the mechanism was wrong but because the move was done halfway. A profile created on Tuesday and populated with two of eleven logins produces the worst of both worlds: two places to look and no confidence about which holds what. The move is worth doing in one sitting.

Move everything at once

Pick a side for every account before starting. Work in one profile, personal in the other, with no exceptions for the account that seems ambiguous. An account that lives in both profiles will be signed in to the wrong one at the wrong moment, and the entire point of the exercise is to remove that question from the working day.

Make the windows look different

Give each profile a name, a colour and an avatar. On macOS the Dock shows one icon for the browser regardless of how many profiles are open, so the window itself has to carry the signal. The profile chip in the top corner is the only reliable marker, and a colour makes it readable at a glance rather than at a squint.

Decide where links open

This is the step people skip and then blame the profile for. Links arriving from mail and chat open in whichever browser instance the system considers default. Setting the personal browser as the system default and opening work links deliberately, or the reverse, is a decision worth making once. Leaving it undecided means every external link is a coin flip.

Split the extensions

Extensions are per profile, which is an advantage rather than an annoyance. A password manager unlocked against a personal vault has no reason to run on a client's admin panel, and a work profile with four extensions instead of fourteen starts faster and leaks less.

A profile pair set up this way needs no maintenance afterwards, which is the actual test of whether the setup was done properly.

The real cost is the switch, not the login

Once the sessions are correctly separated, the remaining cost is measured in switches per day rather than in accounts held. Someone who moves between identities three times a day loses almost nothing and should stop at profiles. Someone who moves between them sixty times a day is paying a different bill.

Each switch is small and expensive in a way that does not show up anywhere. Find the right window among several that look alike. Confirm the account before typing. Recover the thought that was interrupted while doing so. The last part is the costly one, and it grows with the number of services rather than the number of accounts, which is why adding a third and fourth web app hurts more than adding a second account of an existing one.

This is the point where the useful unit stops being the account and becomes the piece of work. Three apps for one client, held together, remembered across restarts, and reachable without reading a list of twenty services. That grouping model is described on the Workspaces page. For anyone who would rather stay on free and published code first, the closest equivalent and its limits are set out on the Ferdium comparison page.

Choosing by frequency rather than by count

A short decision path covers most situations.

Two accounts of one service, used occasionally: use the service's own multiple sign in and accept the link routing problem.

Two accounts of several services, used daily, on Firefox: containers, with routing rules set for the domains that matter.

Two accounts of several services, used daily, on a Chromium browser: a second profile, named and coloured, with every personal login moved into it in one sitting.

Many services, many identities, all day: the browser has already done its part. What remains is arrangement, and no amount of session isolation will fix it.

What to change first

Create one additional profile today and move every personal login into it in a single sitting, then work that way for a week without adding anything else. Most of the confusion disappears at that step, and whatever still hurts is a precise description of the remaining problem. If what remains is arranging windows rather than separating logins, compare that against SpaceDeck rather than against another extension.