Have a look at the following question for a possible solution for the problem:

warn when closing multiple windows

Thanks for your response. When I go to the GENERAL tab in Firefox preferences, the " Show my windows and tabs from last time" is not even an option, as it is grayed out. Instead I have "Show my home page". I don't have any "tab-related extensions" that I am aware of. Everything else is good so I don't want to go to the trouble of "installing one of the many 'give me an extra warning' extensions". It would be my luck that it would give me other changes that I don't want and may or may not solve my initial problem. I guess I'll just have to open multiple windows instead of multiple tabs. This feature used to work for me and I'm not sure when it quit working, most likely with an update(?) It's irritating but I guess I'll have to learn to live with it. I don't know why the check box is in Firefox preferences if it doesn't work. Thanks for your time and trouble.

Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"

This worked for me. Thank you so much!

PROBLEM: Windows FF 21.0 warns when closing multiple tabs when ONE occurance of FF is open, but NOT when mutlipe windows are open (then it only warns once I'm down to 1 window open).

I would like a warning for ALL windows' multiple tabs. I know this is possible because that has always been the case until approx. the latest update.

Oddly enough, the only thing close I found is a post from 2011 with the exact opposite problem: warning only when multiple windows are open, but not when 1 window is open.)

SUMMARY attempts gleaned and compiled from the various posts (with no effect):

- at General tab, "Show my home page" is selected ("Show my windows and tabs from last time" is NOT selected)

-at Tabs tab, "Warn me when closing multiple tabs" is selected

- at Privacy tab, "Use custom settings for history" is selected along with "Always use private browsing mode" (is selected); however, this has always been my setting, and I've always received warnings in multiple windows until recently

- staring in Safe mode had no effect

- my about:config boolean settings are appropriately set to true/false

- I've tried restarting Firefox multiple times and restarting the computer; I have not re-installed FF nor restarted from fresh, wiping out all settings because I have so many customizations.

Any other thoughts of what I might try?

Does it work if you are not in Private Browsing mode (i.e. is only happens in PB mode with the current setup)?

Current Firefox versions may behave differently with the change to a New Private Window.

Yes, when I UNCHECK Private Browsing, it works. However, the glitch with that is that the next time I opened FF, I got blasted with literally non-stop cookie permission requests, to the point that I had to Ctrl-Alt-Delete to close FF, then (after several attempts) QUICKLY get to the Tools page between pop-ups to select PB again. It's not so bad. I'll simply live without warnings when multiple windows are open. Not worth UNdoing Private Browsing! Sheesh.

Are you using the cookies setting "ask me every time"?

It is usually best to avoid this setting as it also may not work properly in some cases with sub domains.

Let all cookies expire when you close Firefox.

• Firefox/Tools > Options > Privacy > Cookies: Keep until: I close Firefox

Create an Allow cookie exception for cookies that you want to keep.

• Firefox/Tools > Options > Privacy > Cookies: Exceptions

You can inspect and manage the permissions for all domains on the about:permissions page or for the current domain via the "Site Identity Button" (globe/padlock) on the location bar and click "More Information" to open "Page Info" and go to the Permissions tab.

• https://support.mozilla.org/kb/how-do-i-manage-website-permissions

You can delete the permissions.sqlite file to reset all permissions.

No, it was not set on "ask me every time" with the option to have cookies deleted at closing. I have since reverted back to simple Privacy Mode, with cookies enabled, but now oddly enough still get constant cookie requests (which I've never gotten before) from sites such as google and safebrowsing, even when I'm not trying to open google or am not in safe browsing mode. I have restarted the computer, and still get constant cookie requests. sheesh. That has been happening now since I turned off the Private browsing to test the tabs issue.

Thank you for the link above, though; very helpful insight.

I'm not sure what you get.

Do websites complain that cookies are disabled?

• http://kb.mozillazine.org/Websites_report_cookies_are_disabled

No, no complaints. Just a pop up window explaining that X site is requesting permission to install cookies, despite me having all cookies already enabled. This was after having restarted the computer. Oddly enough, the problem has not ocurred today--so, the computer had a chance to "rest" over the weekend, and I believe a power failure also shut it off completely for a few days. I will consider this case closed, and the mutliple-tabs warning a sacrifice of using Private Browsing. Thank you for all your suggestions and the included links. Very insightful.

You (will) get this pop-up asking for permission to store on a lot of sites because of legal issues sites need to ask permission if they want to store cookies, so don't worry.
There is usually no need to deny this request.

Ok, that's good to know, thank you. Odd though--I don't remember ever getting them before, and now they seemed to have stopped again. Perhaps interaction with fluctuations in our server firewall and settings too.