I have the same experience with all Khan Academy videos after having upgraded the channel to version 12.
Have tried with multiple versions of Firefox and also Kolibri 0.10.0 and 0.10.1 .
Is this supposed to be reported elsewhere as it seems something specific to Khan Academy (en) videos.
Saw Laura’s response at Kolibri v0.10 has been released!. The suggested solution is for Linux but we are experiencing this issue on Windows as well as Linux.