Bowser vendors including Mozilla and Opera recently agreed to implement support for WebKit prefixed CSS properties in order to improve web compatibility specially on the mobile platforms. This was a huge step towards bringing advanced CSS features across mobile and desktop browsers. But now, it seems that this major change is not going to perform as expected. A primary analysis by Mozilla engineers indicates that there is a very small benefit of adding WebKit CSS aliases, at least to Gecko, the browser engine of Firefox and other Mozilla-based browsers.
In the above analysis, Mozilla team tested several web sites known to use the WebKit CSS properties using Firefox Mobile builds (with original User-Agent and spoofed iPhone UA, with and without aliasing) and Safari on iPhone. The sites having heavy use of WebKit CSS animations and transitions showed noticeable improvements, while other sites rendered without any noticeable issue. These tests were focused on User-Agent sniffing and aliasing prefixes.
The team will continue its tests with considering DOM/WebAPI aliasing and other missing CSS/DOM/WebAPI features in Gecko, which will finally clear the situation. Detailed test methodology and list of aliased properties can be referred here.