There're seems to be a problem regarding the download link in the buffalo website (US).
If you select "By Product Name" then select "WHR-G125* Highspeed Broadband Router and Access Point With High Gain Antenna".
The firmware download would be v1.40 and for WHR-G54S
but if you select "By Product Mode" and select "WHR-G125" it will give you the exact firmware for WHR-G125.