If "Show windows and tabs from last time" then you likely won't be asked for confirmation and yes that is the preferred setting to avoid problems with restoring a session is case of problems with crashes or other restart reasons like an update.

You could keep another window open and use History > Recently Closed Windows to reopen that accidentally closed window. Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

Thank you cor-el, for your prompt and comprehensive reply. I understand the programming need you mentioned for having windows and tabs restored on restart, and my windows and tabs do exactly that; they all come back as they are directed. My problem is solely on account of the limitations of dial-up internet access, basically it is brutally slow and has been known to go to sleep with very little encouragement. On high-speed, reopening oopsie tabs closed in error is no more than a blink or two. The same reopening of 10 or 12 tabs via dial-up would, conservatively, consume the best part of a half hour! My inbox (one of the tabs) usually exceeds a full 10-minutes to finish drawing, and depending on how graphical the other tabs are, there is a heap of waiting while pages redraw. My problem is how to intervene in a Firefox close/exit command by means of a dialogue box telling me not to be an idiot, and without losing the very valuable restore windows/tabs setting.

Maybe hide the Close button with code in userChrome.css.

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#titlebar-close { display:none !important; }

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

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

Wow, cor-el, I like it! Bit hard core for me, but if I muster the necessary courage, I am game to give it a try. Any chance the programmers of the finest browser this side of the Andromeda galaxy, could be convinced to add this wonderfully slick solution as an (strange) option in a future release? High-speed users would scratch their heads at the peculiar notion of hiding the X, but for those of us condemned to suffer the vagaries of dial-up, it is a boon. As I write this, my anti-virus is updating 89MB; been chugging for 4-hours, and estimates more than another 7-hours to go. Is the X just hidden, or is the space it formerly occupied also disabled?

• Create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• Use a plain text editor like Notepad to create a (new) userChrome.css file in the chrome folder (file name is case sensitive)
• Paste the code in the userChrome.css file in the editor window
• Make sure that the userChrome.css file starts with the default @namespace line
• Make sure that you select "All files" and not "Text files" when you save the file via "Save file as" in the text editor as userChrome.css.
  Otherwise Windows may add a hidden .txt file extension and you end up with a not working userChrome.css.txt file

cor-el, your specific directions (even for case sensitive and lower case) inspire confidence. When the anti-virus update is finally finished doing its thing, I shall close Firefox, copy my profile (in case I mess up), follow your instructions, cross my fingers and watch my X disappear. Thanks, again, your solution is nifty and involves thinking outside the box.

For other readers considering enacting this, I should add that my "copy profile" step is a very easy method of recovering from errant keystrokes. Menu Help, Troubleshooting Information, Profile Folder and Show Profile locates and opens that vital folder. Just built a new puppy, and successfully migrated both Firefox and Thunderbird to the new machine, bookmarks, address book, passwords, everything operating just the way it was on the retiring computer. Wonderful.