Hi Huaidan, welcome to Synfig
No, there is no scripting interface for the moment in Synfig. There are several convert types for the parameters of the layers that allows produce powerful parametric animations. See the Particles templates I did some time ago.
Regarding to a plugging for the browser to interpret native synfig files, no, there is not plan for that at the moment. Consider that we are joining all our efforts to the most important missing features in Synfig and our resources are quite limited.
Youโre invited to join us to contribute to improve Synfig in any of its aspects. See my signature