The text input box in my Firefox 60 has dark text on a black background (see below)

Screenshot-from-2018-06-20-21-36-57

The reason is I'm using a dark theme called Adwaita-dark on Ubuntu 18.

Screenshot-from-2018-06-20-21-34-49

It turns out to be a generic problem people are facing. I'm sure someone will fix it down the road but here is the quick fix if you can not wait:

1.Create a desktop icon:
gedit ~/Desktop/Firefox.desktop
2.Fill the following content & save the file.

#!/usr/bin/env xdg-open
[Desktop Entry]
Version=1.0
Type=Application
Terminal=false
Exec=env GTK2_RC_FILES=/usr/share/themes/Adwaita/gtk-2.0/gtkrc GTK_THEME=Adwaita:light /usr/bin/firefox
Name=Firefox
Comment=Firefox
Icon=firefox
  1. Right-click on the Firefox icon you just created on your desktop and click:
    Properties -> Permissions -> Allow executing file as program
  2. Double-click the Firefox and click Trust and Launch (you only need to do this once).
  3. Done, enjoy the dark color text on white text inputs.
    Screenshot-from-2018-06-20-21-53-17