Extension to invert colors, reduce contrast for Firefox

Inverts page colors, showing white text on a dark background, to reduce eye strain.

Works especially well for people working during the night or in low light environments.

Click the button in the icon bar to switch between the supported modes:
* Mode 1 (default): invert colors and reduce contrast
* Mode 2: invert colors, normal (high) contrast
* Mode 3: reduce contrast only
* Mode 4: disabled.