In firefox you come on websites like youtube where you need to type in your name or a description and the inputbox is nearly unreadable.
The fact that it is unreadable might be due to the settings of the dark theme you are using. I am using the Arc theme from horst3180 and this is the fix.
We download from this github
git clone https://github.com/arcolinuxd/arco-xfce
and run one script to fix the issue in the folder personal. Mind you. First startup firefox then run the script.