To get the latest Flash player for Firefox on my Kubuntu 8.04 Hardy system I went to Adobe's site and downloaded the file
install_flash_player_10_linux.tar.gz. As root I untarrred it into the Mozilla plugins directory. When done I had the file
/usr/lib/mozilla/plugins/libflashplayer.so.
I understand that the location to use may vary between Kubuntu releases, and between distros. You can find the directories you Firefox is loading plugins from by entering
about:plugins into the location bar. This lists all active plugins and where they are loaded from.
You can check what version of Flash is active in your any web browser by going to the
About Flash page on Adobe's website.
Hope that may help someone else who is having problems with Adobe Flash player.