The Mozilla Layout, QA, and Market Insight teams recently analyzed the impact of aliasing Webkit CSS properties in Gecko with the goal of answering the question,
Does aliasing a subset of Webkit CSS properties in Gecko improve mobile Web compatibility?
The results thus far indicate that there is a very small benefit of adding Webkit CSS aliases to Gecko. However, our research is not yet complete, so we will refrain from making any definitive decisions until all our research has been carried out.
The consensus from dbaron, jet, jsmith, tchung, aaronmt, jjensen, and me is that the value of aliasing Webkit CSS properties in Gecko alone appears to be pretty low and the benefit does not warrant its inclusion in the platform at this time.
I have posted an overview of our analysis, which led us to reach this initial conclusion, and the next steps for our investigation in the dev-platform group.