There is out v.406 . And as Adobe for Linux only provides security updates ....
If you can't wait until available in Debian and you want to install it manually, you need to change ownership to root:root after you untared and before you copy the files and folders.
# 32 bit
tar -xf install_flash_player_11_linux.i386.tar.gz
chown (-R) root:root libflashplayer.so
chown -R root:root usr # no "/" in front od usr
chown (-R) root:root readme.txt # you won't copy it, so I mention it just for completeness
cp -r usr/* /usr
cp libflashplayer.so /usr/lib/flashplugin-nonfree/
# 64 bit
tar -xf install_flash_player_11_linux.x86_64.tar.gz
chown (-R) root:root libflashplayer.so
chown -R root:root usr # no "/" in front of usr
chown (-R) root:root readme.txt # you won't copy it, so I mention it just for completeness
cp -r usr/* /usr
cp libflashplayer.so /usr/lib/flashplugin-nonfree/