Comment 13 for bug 74360

Not with Firefox, but with other applications such as gedit and
gnome-terminal, there *is* a graphical way to change your input method
temporarily to the X input method. Right-click (if your pointing device is
set for right-handedness :^]) in the text input field, and choose Input
Methods and then X Input Method (or Input Methods and then System to return to
the GNOME input method). With the X input method, if your locale allows it,
you will be able to enter “ (LEFT DOUBLE QUOTATION MARK) by tapping
Compose·<·" (or Compose·"·<), but you won’t be able to enter it by tapping
Ctrl+Shift+U·2·0·1·C·Space. This setting will persevere for this one
application session.