The -moz-opacity property of an image is used to set the opacity of an image. This property is used to create a transparent image in Mozilla. IE uses filter:alpha(opacity=x) to create transparent images.
Example
You can try to run the following code to style an image and set opacity with CSS
<html> <head> </head> <body> <img style = "border:1px solid red;-moz-opacity:0.2;filter:alpha(opacity=50);" src="https://www.tutorialspoint.com/assets/videotutorials/courses/css_online_training/380_course_215_image.jpg" /> </body> </html>