The latest version of Firefox (v.4) had some quirks in its default setup, most notably for me being the loss of saved tabs — previously, the browser would (upon Quit or shut-down) allow me to choose to Save Tabs for restart/reopen, or choose to allow them to go by the wayside and start fresh… with the new installation, that option suddenly went bye-bye…

Here’s what I did, thanks to some savvy users/developers and their forum notes online…

Type: about:config into the URL (web page “location”) bar in Firefox, and you’ll get a slew of commands. You’ll need to locate 4 of them:
browser.tabs.warnOnClose
browser.warnOnQuit
browser.warnOnRestart
browser.showQuitWarning

After locating them all, see which ones were not marked True — by double-clicking individual lines which are marked False, they will become True statements and activated as such. Looks like the default upon install was set (for some people?) to False.

Hope this helps someone else before they get frustrated and reinstall v.3!