This has nothing to do with Facebook. I'm getting the same problem, it happens if you press F5, then subsequently press Alt+Tab. Pressing any other key before Alt+Tab avoids the bug.
Also, the keyboard lock can be disabled if you have multiple keyboard layouts by right-clicking on the keyboard icon in the systray and switching to your alternative layout and back.
This has nothing to do with Facebook. I'm getting the same problem, it happens if you press F5, then subsequently press Alt+Tab. Pressing any other key before Alt+Tab avoids the bug.
Also, the keyboard lock can be disabled if you have multiple keyboard layouts by right-clicking on the keyboard icon in the systray and switching to your alternative layout and back.