Let's say you go to Pandora and it says you have to install the Flash plugin. You click on install, and it says it wasn't found and tells you to install it manually.
You go to the website and download flash_player_9_solaris_x86.tar.bz2. Then what?
As root, extract libflashplayer.so from the archive and drop it into /usr/lib/firefox/plugins. Restart Firefox and you're done =)