Looks like there are a few options available to try - https://addons.mozilla.org/en-US/firefox/search/?platform=mac&q=grayscale&type=extension https://addons.mo

Looks like there are a few options available to try - https://addons.mozilla.org/en-US/firefox/search/?platform=mac&q=grayscale&type=extension https://addons.mozilla.org/en-US/firefox/search/?platform=ma...