As I was working on stylesheet for a upcoming site release at my day job, I ran across the following. As of the Firefox 19 release, Mozilla has changed the CSS placeholder attribute, :-moz-placeholder. Until now, the placeholder attribute could be targeted in the Mozilla Firefox browser with one colon. Whereas now, the attribute must be preceded with two colons to look like the following, ::-moz-placeholder. Time to start updating stylesheets, and hammering the above into our developer minds.
The above documentation can be found on the Mozilla Developer Network under Firefox 19 documentation.