It seems to be connected to "remember history". When I select "don't remember history" in the privacy tab, the pop-up warning is not shown even if the option "warn me when closing multiple tab's" is selected. (FF4.01) Probably an error?

I'm using 3.6 and it doesn't work. The thing is when I open a site (any site including the name firefox or mozilla like the "help" tab in the tools/options of firefox), and then I close the windows, it automatically asks me if I want to close all tabs! But when I try again and again with other windows (without sites with mozilla), it doesn't work. I don't know why. I chose the "use custom setting for history" in the privacy tab. Does it affect? Thank you!

You can set the warn prefs on the about:config page to true via the right-click context menu or toggle the value with a double left-click.

• browser.tabs.warnOnClose, see http://kb.mozillazine.org/About%3Aconfig_entries
• browser.warnOnQuit , see http://kb.mozillazine.org/browser.warnOnQuit
• browser.warnOnRestart , see http://kb.mozillazine.org/browser.warnOnRestart

Firefox 4 has this pref in addition to the above listed prefs:

• browser.showQuitWarning, see http://blog.zpao.com/post/3174360617/about-that-quit-dialog

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.
You can use the Filter bar at to top of the about:config page to locate a pref more easily.

Thanks cor-el, but it did not work for me. Via your links I found https://bugzilla.mozilla.org/show_bug.cgi?id=419009#c139 where the interaction with te privacy settings is noted. So uncheck "permanent privacy mode" to get the warning, uncheck the first 3 sub-options, check the sub-options for cookies and history and check all options in the settings for history - and the warning still works.

Firefox will never save any data from current session to disk if you are in Private Browsing mode, so you won't get a warning if you close Firefox in Private Browsing mode.

I think there are not many people who find it evident that saving data to disk and warn when closing multiple tabs are the same thing or are necessarily related. If it was not mentioned by cor-el, I even would not know now that in "Private Browsing mode" Firefox never saves any data to disk.

See this article for information about Private Browsing

• Private Browsing - Use Firefox without saving history

@ cor-el

And where in that article it says that "warn me when closing multiple tabs" shouldn't warn you when you are in Private Browsing mode ?

Stop being apologetic for Mozilla, it's clearly a bug, at least 8 months ago you knew about same problem on 3.6.x and I still have it on 3.6.17.

(I check the option, it works for a while until it doesn't. Mac OSX.6.6)

P.S. I never ever use Private Browsing.

See also:

• How do I restore my tabs from last time?