Hello MathU41,

You may have the values of those preferences set to "true", but you won't see that warning if you have Firefox set to restore previous session ....

Would you check this please :

3-bar menu (or Tools) => Options => General, under "Tabs":

Restore previous session and : Warn you when quitting the browser

If you do want Firefox to restore your previous session (and get the warn on close warning as well), then make sure that both boxes are checked.

Neither were checked. Checking both doesn't seem to prompt the warning, either.

MathU41 said

Neither were checked. Checking both doesn't seem to prompt the warning, either.

Cancel that, now it does give me a warning, but only when I have like 30 tabs open--I presume more than the 'recently closed tabs' in History retains.

MathU41 said

browser.tabs.warnOnClose and browser.tabs.warnOnCloseOtherTabs are set to 'true'.

Did you have to change those values yourself, and if so : did you close and restart Firefox after you made the change(s)  ?

I did not. I did toggle them to false, checked, and returned them to true. Firefox has restarted since.

I have absolutely no idea why you don't get the warning - I'm hoping that somebody else does (sorry ...)

MathU41 said

Cancel that, now it does give me a warning, but only when I have like 30 tabs open--I presume more than the 'recently closed tabs' in History retains.

Just a thought :

On the "about:config" page, would you check the value of this setting please :

browser.tabs.MaxOpenBeforeWarn (default = 15)

Indeed, it's at 15. Thought that was about opening tabs, though, and didn't occur it might mean anything about closing them.

McCoy said

MathU41 said

Cancel that, now it does give me a warning, but only when I have like 30 tabs open--I presume more than the 'recently closed tabs' in History retains.

Just a thought :

On the "about:config" page, would you check the value of this setting please :

browser.tabs.MaxOpenBeforeWarn (default = 15)

Unfortunately, it does not working. I have the same value in about:config, but when closing more than 15 (for example 22 tabs), warning still does not appearing.

This is about being able to use "History -> Recently Closed Tabs/Windows" to recover tabs. The maximum for undo (reopen) tabs has been changed to 25. So only if you would close more than 25 tabs to get a warning.

• browser.sessionstore.max_tabs_undo
• browser.sessionstore.max_windows_undo

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config