GetPrefForDriverVersion takes a narrow string, and the caller widens it. But SetPrefForDriverVersion takes a wide string. In bug 656826 the function was simplified but it ends up setting the preference as a UTF8 value rather than the ASCII value that the caller of GetPrefForDriverVersion expects it to be. Now I wouldn't be surprised to learn that the string was indeed ASCII and it therefore makes no difference which conversion you use, but I think it would look better if the various methods were consistent. In fact the methods are so small it might even be worth inlining them which would also resolve the confusion.

GetPrefForDriverVersion doesn't exist any more.