I tried Conn's flashplugin-nonfree package in comment #23, and it doesn't solve the issue for me.
More, epiphany-gecko for some reason seems to present this issue far more frequently than firefox.
Simply browsing youtube a little or opening and then closing a couple of tabs with flash video in them, makes all gecko browsers go down.
Attaching a stacktrace for epiphany (the one for firefox is mostly identical to the one already provided).
This happens on the website onepieceworld.net, simply waiting for the page to load and scrolling it for some time. But it happens also on a lot of other websites, too.