Letterboxing can change by a few px unnecessarily when opening find bar.

Steps to reproduce

1. Open a web page.
2. Resize the window so you have some significant letterbox padding at the bottom that can fit the find bar.
3. Open and close the find bar with Ctrl+F and Esc respectively.

Result

The letterbox padding jumps up and down by a few pixels during the transition. This is measurable by window.innerHeight.

Expect

The letterbox size should remain the same whilst the find bar is being revealed or closed.

Cause?

I think this may have something to do with the findbar's CSS transition properties. During the transition the findbar is changing in size.