Brightness filter in firefox and opera without svg file

Question

For my current project i used filter -webkit-filter: brightness(-20%);-moz-filter: brightness(-20%); But somewhy, this filter doesnt works in firefox and

Answer 1

If you need a more cross-browser solution, you could make the images translucent when they are not hovered:

img {
    opacity: .7;
}
img:hover {
    opacity: 1;
}

This will have the effect of darkening them when they are on a dark background.