Hi

Thank you for your question, but this does not sound like an issue with Firefox.

Your monitor or display should have some buttons or controls to allow you to reduce the brightness. I recommend turning it down to make it less painful to use, as often the default settings are set very high.

Read the manual for your monitor. And if you can't find the manual get it from the manufacturer's website using the brand and model information on the "tag" on the back side of that monitor.

The controls are usually on the lower-right front of the monitor or "hidden" in that corner on the bottom of the bezel or frame.

When I got this Acer LED monitor I found it too bright and turned the brightness down to 30% to make it a lot less harsh. It was a lot brighter than my two previous flat screen monitors which weren't LED, which didn't need that much of a "tweak" to make them usable in a somewhat dark room with no overhead lighting.