This may help
https://cameratico.com/color-management/firefox/
First thing I would check is if you have a path specified in Firefox "about
:config" for gfx.color_management.display_profile
If you have a path specified for a previous monitor profile that is no longer valid this may cause the issues you are experiencing.
I use a Eizo wide gamut screen and in Firefox (64 bit) this is my setup:
gfx.color_management.display_profile C:\WINDOWS\system32\spool\drivers\color\CS2730(296 88097)90cd 6500K 2.20.icc
gfx.color_management.enablev4 true
gfx.color_management.mode 1
Finally.....what version of Firefox are you running ?