I have some feedback on this issue. I reverted to FireFox 56 and the issue did not go away.
I have found the culprit however. The download manager I was using in FireFox was not compatible with FireFox 57 so installed Free Download Manager to replace it. This requires installing a browser extension for FDM. There are 2 available.
The “Free Download Manager extension” extension breaks “Select images…”.
The “Download with Free Download Manager (FDM)” extension works and does not break “Select images…”
Everything is working fine now. I hope this helps someone else too.