Annoying automatic scroll in editor mode.

Hi,

since I’ve updated my wp installation to 4.6 I have this problem:

when adding some text in editor mode, the windows scrolls down. The line I’m editing becomes the last row at the bottom of the page. This is quite annoying since I’d like to keep the row, let’s say, in the vertical middle.

Any hint about solving this issue?

(btw I use firefox).

Many thanks in advance.

A.