One browsing context, doing one thing
The condition is about a browsing context: a profile and everything attached to it. Cookies. Stored logins. History. Extensions. Cache. A browser signed in to mail, to shopping, to a forum and to a work account carries all of that into every tab it opens. The stored material is present, addressable and, in ordinary use, useful, which is why it is there.
This card says the window you use for this holds none of it. The distinction that matters is between closed and absent. A signed-in account with its tab closed is still a signed-in account, and a site you have not visited today still has its cookie in the profile. Closing things is housekeeping, not separation.
The word for what this achieves is containment, and it is worth being exact. Containment removes nothing. It draws a line and says what is on this side does not automatically appear on that side. The material still exists. The claim is only that it is not sitting in the same context as the thing you are doing.
Three things this rests on
- The browser came from the Tor Project
- Supplies the enforcement. Separation between contexts is drawn by software, so a profile boundary is exactly as real as the program maintaining it.
- Nobody else can read the screen
- Supplies the physical half. Software separation is defeated by a person at your shoulder, who sees one screen and does not care how many profiles produced it.
- The security level was set before the first page loaded
- Supplies the terms inside the boundary. A contained context still has whatever capabilities it was given, and the level decided those before the first page arrived.
Three upstream edges is the most any card in this stage carries. It is a place where several separate lines converge rather than a step inside a sequence, and each of the three can fail without the others noticing.
The end of a chain, and what that means
Nothing on this map depends on this card. It is terminal. Roots and endings lists the small number of cards in that position, and the position is worth understanding before deciding the card is therefore optional.
A terminal card is one whose failure does not propagate. If this condition is false, everything above it is untouched. A circuit still builds. An address still has the shape it has. A session still logs in a second time. Nothing downstream collapses, because there is nothing downstream. Compare The browser came from the Tor Project, where one failure invalidates four cards at once.
That is not an argument that the cost is small. The cost is real. It is local, and it is permanent in a way most of the reversible failures here are not. A join made once between a browsing context and an ordinary account stays made. You cannot undo it by opening a different window afterwards, the way you can restore a circuit by correcting a clock.
| What it costs | Where the cost lands |
|---|---|
| The join between two contexts | Local and permanent. Once two things have shared a context, nothing later in the session unshares them. |
| Cards further down the map | None. No condition in the address, session, value, order, parcel or close stages waits on this one. |
| The rest of stage B | Unaffected. The client can build a circuit at all does not care how many accounts the browser holds. |
So the honest statement is that this is a card you can fail while completing everything else on Dependency map. That is why it gets skipped, and why the containment has to be described accurately rather than oversold. A contained cost is still a cost. It is a cost that stops here.
How a shared browser joins two things
Concretely, the failure looks like this. You use a browser signed in to ordinary things. You open a new window in it for this. The window inherits the profile, so the stored logins, cookies, history and extensions are all present in the same place as the tab you thought you had separated.
Nothing appears on the screen. No warning, no prompt, no indication that two things are now in one place. This is the second card in the stage whose failure is completely silent, alongside provenance, and silence is why both get skipped. The failure produces a session that works perfectly well.
If confusion arrives it arrives much later and in a form that does not name this card. Somebody notices two things were connected and cannot reconstruct how. The mechanism was ordinary, boring and invisible at the time, and no error message anywhere would ever have pointed at a browser profile.
Looking at the history and the account list
Open the browser you are about to use. Look at the history. Look at whatever list it keeps of saved logins, and at the extensions. Read all three and ask one question of them: does anything here name me.
- A pass
- The history is empty or holds nothing that identifies a person. There are no stored logins. The extension list is whatever it was on installation, because the profile has never been used for anything personal.
- A fail
- Anything in any of those lists belongs to your ordinary life. One stored login is enough. So is a history entry with a name in it, and so is an extension that keeps itself in step with an account somewhere.
The check opens no address at all. It runs against the browser itself, before anything is pasted into the bar, which puts it in the same family as The security level was set before the first page loaded. Settled offline, settled early, and easy to verify because the evidence is sitting in the interface.
A profile does not become mixed on its own. It becomes mixed the first time somebody signs in to something in it, so passing this check once says nothing about whether it still passes in a month. Whether the separation survives repeated use belongs to You can come back tomorrow and still be you rather than here.
Not a claim about anonymity
This is not a claim that separate browsers make anybody anonymous, and nothing on this site makes claims of that kind. It removes one specific way of joining two things together and leaves every other way open. The adjacent idea usually substituted for it is private browsing, which is about what is kept after a window closes rather than what is present while it is open.