Revert 2c7bebb5f2c873850c2b2d82013cab4eb3d4913c

On reflection, this seems too dangerous:

   - Somebody excluded flash for a reason, and without knowing that
     reason, it seems dangerous.

   - Imagine a flash game with key bindings.  Perhaps it uses ? to
     show the key bindings, and ESC to hide them again.  With
     2c7bebb5f2c873850c2b2d82013cab4eb3d4913c, you can never hide the
     key bindings (I think).

All in all, this just seems too risky.