New forum: "Select" code does not work

[Peter2]

Every code snippet in the forum has a <Select> button on top of the code.

In Firefox 55 (with a lot of plugins and in pure vanilla) it does not work anymore - it only jumps to the top of the page (Win 10 German).

In Google Chrome it works fine.

See screencast: https://www.screencast.com/t/7t7DNvlc