Iceweasel has javascript disabled by default
I am saying the opposite! Stop the blocking of scripts, i.e., enable the scripts, i.e., disable the scripts- and ads- blockers.
And you can understand that some (not all) sites have become inaccessible for your native Flash.
So, that's it. If your flash is old, replace with a new flash libflashplayer.so plugin manually in /home/knoppix/.mozilla/plugins.
Even then, if flash doesn't play for those sites, the sites are doing something complicated & your knoppix is fine!
How could I miss the point?