@Sup3rkirbyJan 30.2015 — #While it's been getting better, a lot of newer CSS properties don't have an official standard that every browser follows. The result is a bunch of browser-specific prefixes for CSS properties (like -webkit, -moz, -o, etc.). In cases like that, each browser handles the property differently and thus you end up with multiple ways to get the same thing.
Generally, the difference is that only one version will work per browser. However, due to browsers slowly updating to a 'standard' version of the CSS property, you'll also find that sometimes there are two ways to get the same CSS effect in a browser. One way is browser specific (using the prefix like -webkit) and the second way is the 'official standard' way, which was likely the newest version added to that browser.