This deprecated, non-standard, property is not recommended. Authors should generally find an alternative way to accomplish the same task while adhering to all best practices, or simply do without it if it is unimportant.
-moz-opacity Mozilla extension property was used as a substitute to the
opacity property. This Mozilla extension is only implemented in Firefox 0.9 and before, and new versions of Firefox no longer support this property. Instead, Firefox supports the
opacity property's values.