1. Pressing 'f' key works ok in any window. It produces an 'f' character. In xev, it produces keysym 0x66 'f'.
2. Pressing 'Ctrl-f' opens an X-Terminal. This happens where ever the pointer is. If the pointer is outside any firefox windows, pressing 'Ctrl-f' still open an xterm. In xev, it produces keysym 0xffe3 Control_L, but when the X-Terminal window opens, the xev window loses the input focus, so it never sees the 'f' key and there is no 'f' keysym event listed.
Something has defined a Ctrl-f shortcut in Unity that works across all applications.
Also, I am using Unity-2D. I can't use Unity-3D or anything else because they are too buggy in Oneiric on this pc. Maybe that makes a difference.