After having spent a good part of an hour on trying to install the Flash Player Debugger for FireFox on Ubuntu 11 64-bit, I found the following steps worked:

1. sudo apt-get install nspluginwrapper
2. copy libflashplayer.so (from debugger download) to /usr/lib/flashplugin-installer/
3. sudo nspluginwrapper -i /usr/lib/flashplugin-installer/libflashplayer.so
4. restart FireFox

Thanks to: AskUbuntu.com.

Don’t forget to set up mm.cfg.

When all is done, run:

tail -f ~/.macromedia/Flash_Player/Logs/flashlog.txt