Somehow dark GTK themes make it hard to read text fields on Firefox. This called for a fix.

The fix criteria must be that, if at all possible, using an extension should be the last resort. So, what are the options? The quick one would be tinkering with about:config and that is what I did.

I created a new string, called it widget.content.gtk-theme-override with the value Adwaita:light. So, what is happening here? I am telling Firefox instead of using Adapta-Nokto Eta as the GTK theme, it must use Adwaita (light) to render its theme.

Problem solved.