Firefox session cookies

Question

Generally speaking, when given a cookie that has no expiration period, modern browsers will consider this cookie to be a 'session cookie', they will remove the cookie at the end of the browsing session (generally when the browser instance closes).

IE, Opera, Safari and Chrome all support this behavior.

However firefox (3.0.9 latest proper release) appears not to follow this rule, from what I can tell it doesn't expire the cookies when the browser is closed, or when the user logs off or restarts the OS..

So, why does firefox refer to these as session cookies, when they last aparently indefinitely?

Does anyone know how Firefox handles session cookie expiration?

Answer 1

This is apparently by design. Check out this Bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=443354

Firefox has a feature where you close Firefox and it offers to save all your tabs, and then you restore the browser and those tabs come back. That's called session restore. What I didn't realize is that it'll also restore all the session cookies for those pages too! It treats it like you had never closed the browser.

This makes sense in the sense that if your browser crashed you get right back to where you were, but is a little disconcerting for web devs used to session cookies getting cleared. I've got some old session cookies from months ago that were set by sites I always have open in tabs.

To test this out, close all the tabs in your browser, then close the browser and restart it. I think the session cookies for your site should clear in that case. Otherwise you'd have to turn off session restore.

Answer 2

Two ideas :

1. You have a problem with your session manager (the one included in FF3 or one included in an extension, like tabmixplus)
2. Use Firebug + FireCookie (https://addons.mozilla.org/en-US/firefox/addon/6683) to debug !

Answer 3

This should work. I used to be one of the cookie module testers, and I don't think there is any design reason this would behave differently (although if you crash, the session cookies might be designed to live on when you restart...)

Are you viewing the cookies in the "Preferences" menu > "Privacy" Tab > "Show Cookies..." button?

Also, have you tried a new profile?

Answer 4

I disagree with meandmycode above.

The HTTP spec https://www.ietf.org/rfc/rfc6265.txt talks about what a client should do with Set-Cookie headers with Expires:

If the server wishes the user agent to persist the cookie over multiple "sessions" (e.g., user agent restarts), the server can specify an expiration date in the Expires attribute. Note that the user agent might delete the cookie before the expiration date if the user agent's cookie store exceeds its quota or if the user manually deletes the server's cookie.

The logical extension of this is that the ONLY way the server has to require that the browser does not maintain a Cookie on exit is to set no Expires value (i.e a session cookie). If a browser does not honor that semantic then its not honoring the server's response.

Essentially the user agent is deciding to ignore the server request and act as if an Expires value had been set.

Answer 5

This is a bit of a concern in shared user environments. If I set a authentication cookie that is set to expire at the end of the session. This will persist in Firefox after the browser has been closed and another user starts up Firefox. Cookies are set with an expiry date for a reason!

Answer 6

I'm flummoxed that Mozilla have left this as it is for several years.

OK.. so I quit FF and switch off the PC. Next day FF starts and opens the last set of pages (nice handy feature) BUT it restores the sessions and I'm logged back in to sites which have no "save my settings" feature. I know because they are sites I built. Whatever I do with php ini settings the sessions are restored.

They absolutely should not be restored. Pages yes, but sessions with cookie ini set to '0' no.

I don't understand why this is not flagged as a security hole. Sure I can do some additional checking on the server side, to see if a login should be allowed, based on time from last log in, but it shouldn't be needed.

A session should NOT persist. FF is manipulating cookie expiry settings.

Answer 7

In my case, it was because of pinned tabs that automatically restored the session even if this option was disabled in Firefox settings. So if you unpin the tabs, the session won't be restored.

Answer 8

Well it is disconcerting to me. My system is set up so that users can hit EXIT whereby I destroy all session cookies. But if a user closes the browser without actually choosing to Exit, I'd like the session cookies cleared.

I actually tested it with Google Chrome, IE 9, and works fine. But Firefox is reluctant to kill this "session" (as reported by Firebug) cookies.

OK. This is what I did. I chose Exit from FireFox main menu and from then on, did it fine as expected (Dont know why).