IrfanView 4.50 was recently released and, according to its changelog, support for Windows 9x has unfortunately been terminated:
IrfanView 4.44 is, based on changelogs, the officially the last version to support Windows 9x.
A shame as I remember using IrfanView in 2006 when I still used Windows 98 Second Edition. It made me happy knowing that it was still supported.