The most likely cause is color management.

Your JPEG has an embedded ICC profile, and Photoshop/Firefox are color-managed, so they read that profile and convert the image correctly for display. IrfanView and a basic libjpeg-turbo decode may show the raw RGB values without applying the embedded profile, which can make the image look darker or otherwise different.

libjpeg-turbo only decodes JPEG data; color appearance matching requires ICC profile handling on top of that. If your app doesn’t apply the embedded profile and convert to the monitor/display color space (or at least sRGB), it won’t match Photoshop.

The fact that the embedded profile is an "input device profile" rather than a normal output/display profile also suggests this file may come from a scanner or nonstandard workflow, which makes proper color management even more important.

To get consistent results:

• use color-managed software
• convert the image to sRGB if it’s meant for general viewing/web use
• in your own app, read the embedded ICC profile and perform color conversion before display

So the file itself is probably fine; the difference is how each viewer handles the embedded color profile.