Chessboard is too big

Hi, since yesterday, I have the problem with that the chessboard is too big, especially in contrast to other UI elements.

Please see:

My screen resolution is 1920x1080 and the board is too big even for this. I do not use any in-browser zoom (have Ctrl+0). Browser Firefox 37.01

Click the eyeball at the top of the screen and use the slider to adjust the size of the board.

Thanks! But I did not move the slider before!

To make it clear, problem resolved, it is now OK. However, I am not aware of moving the slider before.