Comment 12 for bug 1263249

To be absolutely clear: The keys have to pressed when the focus is in an input field, that is, where you'd normally type something. E.g. a gnome-terminal. Pressing Ctrl+Shift+U enters a special mode where you type a Unicode character by its hex code. If you type at most 6 digits and then press Enter or Space, the typed value is converted to a Unicode character of that codepoint. E.g. press Ctrl+Shift+U, type 4000 and press Space, you'll see a Japanese or Chinese (I don't know, sorry) symbol. But if you press Ctrl+Shift+U, followed by 7 digits, you'll see a nasty lockup. (Be sure to save all your data before!)