Comment 1 for bug 202722

Here is a workaround for all you hardy / firefox-3.0b4 users. This will also work with other versions of firefox. Just change the destination directory.
The problem is that firefox is using "/usr/lib/firefox-3.0b4" while gnash is installing to "/usr/lib/firefox". I am sure once hardy is released firefox will again use "/usr/lib/firefox".

NOTE: Also remove any other files with "flash" in the name from the "/usr/lib/firefox-3.0b4/plugins" before running the command below to remove any previous installs of Adobe flash.

sudo cp /usr/lib/firefox/plugins/flashplugin-alternative.so /usr/lib/firefox-3.0b4/plugins/

Good Luck and happy youtubing