Firefox suddenly defaults to flash again on youtube

[Tim]

Allegedly, on or about 03 November 2015, Heinz Diehl sent:
> Where is the config option, switch or whatever changes the default
> player in firefox back to html5 again?

What's the difference between the two user profiles?  Accepting/refusing
cookies (could try clearing out the stored cookies for YouTube)?
Allowing/refusing scripting?  Flashblock options?  Logged into YouTube?

-- 
[tim at localhost ~]$ uname -rsvp
Linux 3.9.10-100.fc17.x86_64 #1 SMP Sun Jul 14 01:31:27 UTC 2013 x86_64

All mail to my mailbox is automatically deleted, there is no point
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public lists.