Why are you saying «browser»?

opera should support webkit prefix

hdias, yes, but this is only true for the latest builds of "presto".
theaqua, it is your religion?

@Gemorroj: Its not about just transitions...but transitions on pseudo elements. I don't think thats supported yet?

@Gemorroj: Opera have removed its transition prefix; checkout the table in this article - http://my.opera.com/ODIN/blog/opera-mobile-12-1-with-spdy-web-sockets-flexbox-and-more

New versions presto, the prefix-webkit supported. http://www.opera.com/docs/specs/presto2.12/css/o-vendor/
In older versions do not. http://www.opera.com/docs/specs/presto2.11/css/o-vendor/
If you add support-o-prefix, it will support older versions of Opera.

Older versions of Opera don't support transitions on pseudo elements.
http://css-tricks.com/transitions-and-animations-on-css-generated-content/

No need to implement this yet, as no version of Opera supports transitions on pseudo-elements.
The -o-transition prefix is not necessary, as only future versions of Opera can support this feature (transition on pseudo) and they are going to also support the prefix-less version of transition.

Indeed, there is a problem with the pseudo elements.