Same problem here with ACF Pro 5.7.2 and Firefox ESR 52 or the latest Mozilla SeaMonkey (2.49), which is based on Firefox 52 (ESR). (Windows)
It works with Firefox 61 and Chrome 67.
No we use version 5.6.10 (thanks for the link, @darrigan).
Please fix this for 5.7.x, thanks!
