Implicitly specify `opacity: 1` for input placeholders in Firefox
Implicitly specify `opacity: 1` for input placeholders in Firefox

When overriding a mixin in SASS, the original rules aren't copied.
This caused issues with the color of input placeholders in FF.

https://github.com/twbs/bootstrap/blob/10606a73bcbfc6c723d60e2a1069c921afff0d2a/less/mixins/vendor-prefixes.less#L105

sg00dwin/patternfly,sg00dwin/patternfly,sg00dwin/patternfly