I cannot say that this is my problem, but it describes it pretty well.
Look at what it says in this article from 2015.:
Firefox then and now, or the difference black point compensation makes
…
As of 2015 and version 31, Firefox still doesn’t support black point compensation, which means that if . . .
- you have properly calibrated and profiled your monitor, and your monitor has a reasonable black black point
- you have your color managed image editor set to use relative colorimetric intent with black point compensation for display to the monitor
- you produce a finished image ready for display on the web
- you view the finished image in Firefox
. . . then as displayed by Firefox the shadows in your image will be more or less crushed compared to how the same image is displayed in your color managed image editor.
Black point compensation “compensates” for the fact that monitors can’t display “no light”. Without black point compensation, all shadows darker than the darkest dark your monitor can actually display are simply crushed to solid black. In a high key image image or an image that has few important shadows, you might not notice any difference. In an image that’s supposed to have rich dark shadows, the difference can ruin your appreciation of the image as all the shadow detail turns to muck.