Bizarrely, I’ve noticed that the Canonical-supplied Adobe Flash 10 plugin isn’t working as well as the Adobe-supplied version.
You could regard this as a possibly moronic statement at first, but there’s a little evidence to back it up. Firstly, I’ve been using the ‘adobe-flashplugin’ package provided via the Canonical Partner repository for some time. I think it works a heck of a lot better than Flash 9, and I’ve been much happier with the experience. That isn’t to say that it’s perfect, but at least Firefox doesn’t crash with every 3rd/4th Youtube video I play.
By standard of course, the Canonical Partner repository is disabled within a fresh Ubuntu installation. So when my girlfriend mentioned that the videos on Llewtube.com weren’t displaying, I wasn’t surprised to find that she was using the latest version of the ‘flashplugin-nonfree’ package:
sudo dpkg -l | grep flash
ii flashplugin-nonfree 10.0.22.87ubuntu1~intrepid1 Adobe Flash Player plugin installer
Given that I could view the videos on the aforementioned website without a single issue, I went to check my plugin version:
ii adobe-flashplugin 10.0.22.87-2intrepid1 Adobe Flash Player plugin version 10
So we’re supposedly using the same version of the Flash plugin, but from different packages. Would anyone like to explain why one package works and the other does not?
Getting around the problem was a simple task for her: simply enable the Partner repository by navigating to the Software Sources configuration utility (via System -> Administration -> Software Sources) and (after giving your password) checking the two ‘partner’ lines under the Third Party tab. If you don’t have them, you can add them (one at a time) with these two lines:
deb http://archive.canonical.com/ubuntu intrepid partner
deb-src http://archive.canonical.com/ubuntu intrepid partner
(If you’re reading this, and you’ve not yet upgraded to Ubuntu 8.10; the bulk of this guide should work with 8.04 also. You will, however, need to swap out ‘intrepid’ for ‘hardy’! 
)
When you’ve enabled the partner repositories (check the boxes) it’s a matter of closing Software Sources and letting it reload the package sources when prompted. After that, simply open a terminal and paste in the following:
sudo apt-get remove --purge flashplugin-nonfree && sudo apt-get install adobe-flashplugin
If you restart Firefox, you should now be sorted. If in doubt, search in Synaptic (System -> Administration -> Synaptic) for ‘Flash’ and see what is (or isn’t) installed.