This randomly happened over the past few months but last couple days it's bad. The Google Sheets cells I have open on Firefox turn black. You can scroll and they will come back but just briefly and back to black. Very annoying as these are shared sheets for my business with other employees. It's not happening in Vivaldi Browser or Edge. I hate Chrome so not even trying it there but guessing it's fine. Seems to just be Firefox all of a sudden. See pic. Help please as I have no clue what's causing this.