That is not possible as far as I know.

Can't you close all open tabs via the Ctrl+W short cut or by middle-clicking the tab?

You can try to temporarily disable JavaScript to see if that allows to close the window.

• QuickJava: https://addons.mozilla.org/firefox/addon/quickjava/

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Could you describe the scenario in a little more detail? Does Firefox just ignore clicks on the red "X" or do you get a message saying that you are not allowed to close the window or does Windows add "Not Responding" to the title bar of that window when you try to close it? Et cetera.

Clicks to close the window are ignored. There is a message that gives a choice to leave the page, but when you click on it it simply reposts the same message over and over again. The only way I can close the window is use ctl-alt-delete and shut down FireFox losing all my other open windows.

Try to toggle the dom.disable_beforeunload pref on the about:config page.

You can open the about:config page via the location/address bar and you can accept the warning and click "I'll be careful" to continue

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

Is this like that scam from last year where you get "trapped" in a page? You could try this:

If you haven't already installed it, open a new tab (Ctrl+t) or new window (Ctrl+n) and go to my bookmarklet page:

http://dev.jeffersonscher.com/bookmarklets.html#escape

If you do not normally display the Bookmarks Toolbar, you can add it to (or move it to) the Bookmarks menu. Hopefully you won't need it very often, or perhaps ever again.

To quickly show or hide the Bookmarks Toolbar, you can use the Bookmarks button on the main toolbar, or right-click a blank area of the tab bar, or the new tab ("+") button.

Then switch back to the un-close-able page and click the Escape button.