A few thoughts,
Was black point compensation ticked in export?
What version firefox are you using? Firefox 77 had a bug which disabled color management for certain images. Firefox 78 fixed that, but can show some color distortion on images with v4 profiles. Here’s some steps to ensure Firefox color management is set up correctly: How to configure Firefox color management
Can’t help what others are doing. Can only ensure things are optimal at your end, but srgb v2 profiles should display correctly on most monitors.
Does this use Wayland or Xorg? Wayland has some color management issues that may or may not apply here: Wayland color management - #508 by gwgill