Is Color Opacity not working in all browsers?

In some browsers like Mozilla Firefox, color opacity will not support.

So, there is a shortcut to include this functionality along with colors. That is, add opacity along with color code.

Example:
color: #ff000;
opacity: 50%;

So, you can add color: #ff000050;

This method can also implement with RGBA color code.
rgba(255, 0, 0, 0.5);