GStreamer in Firefox disabled

[Llorephie]

Hi, I'm trying to use RPi2 as desktop, and yesterday I've found one problem - there is no GStreamer support in Firefox build in armv7h, so it is impossible to play MP3 embed audio in HTML5 <audio> tag (all other formats looks like work), and chromium build doesn't work yet.
GStreamer looks like disabled in build, but looks like work in system now. Is it possible to rebuild package on Pi2 w/o disable flag?