This bug was filed from the Socorro interface and is report bp-92f7b1ec-a60d-40bc-951c-4d0442160416. ============================================================= 8 crashes with this signature have been seen, the first occurring in Nightly 20160415030231. The diagnostic assertion triggering the crash was added by bug 1258768.

nical, can you please investigate?

This happens after a device reset. We have hardware decoded video frames still in flights and they are received by a BasicCompositor rather than a D3D11 one and that's what causes the assertion to blow up. In release, the diagnostic assert will just return null and the caller null-checks so we'll be good. I'll have to replace the assertion with a warning for beta/aurora users for now because it is hard to prevent this situation to happen when having a device reset. More worrying: this means that before bug 1258768 we were potentially unsafely casting a BasicCompositor* into a D3D11COmpositor* if having a device reset while playing a video, so we need to patch that up and uplift it.

Has not occurred in versions after Nightly 20160422030223. Thank you for the fix.