Upgrading 64-bit Flash for Iceweasel
Two Issues
The two issues as it turns out:
- first, the default download of the Flash plugin for Linux is 32-bit and my OS is 64-bit;
- secondly, being Debian it's Iceweasel, not Firefox.
Solution
Find the 64-bit .tar.gz download, unpack then copy libflashplayer.so to
/usr/lib/iceweasel/pluginsnot
/usr/lib/firefox/pluginsand restart.