Launch mozilla (latest nightly build as of 23 Feb 2001), and use some menu commands to make sure they work. Then close all windows, including bookmarks, browser, etc. You can still select menu commands (new window, manage bookmarks, etc.), but nothing happens. Keyboard commands don't work either. If you send an AppleScript command to the browser, it works, however. (For example, tell application "Mozilla" openurl "http://www.apple.com" end tell) Once the new URL opens, you can continue using Mozilla as usual, as long as you keep at least one window open at all times.
dupe of bug 68766 Closing all windows causes Mozilla stop responding *** This bug has been marked as a duplicate of 68766 ***