$ ls -l ~/.mozilla/plugins
-rw-r--r-- 1 simon simon 856 2008-05-10 04:27 flashplayer.xpt
-rwxr-xr-x 1 simon simon 7040080 2008-05-10 04:27 libflashplayer.so
... that is my working configuration. Installed from firefox - click on the non-rendering player and then select "install plugin". Also does this with the apt-get method. No idea what you
are doing to get different files.
To be non-ambiguous - reproduce the above command then paste the command, together with the output, like I did. Bear in mind that that first $ sign is the prompt. The command is:
ls -l ~/.mozilla/plugins