The first crash signature (F1776344327) is the most interesting, but it's super rare. The second crash (F1398665248) is just the generic "Flash went away unexpectedly" signature. It happens for a whole list of reasons, but most commonly because some inter-process communication between Flash and Firefox has detected a hang after 30 seconds, or we've run out of memory or decided that something that the content has asked the VM to do looks like might be malicious, and we pulled the emergency stop instead of trying to risk it and continue.
I'd really like if you could provide the content of about:support and about:plugins.
Thanks,
Jeromie