Windows 10 Pro x64, IrfanView 4.40 x64: If you make the open file dialog window larger, it's not possible to make it smaller.
Workaround: delete HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\Curre ntVersion\Explorer\ComDlg32\CIDSizeMRU.
Workaround: delete HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\Curre ntVersion\Explorer\ComDlg32\CIDSizeMRU.