So I upgraded to Karmic and Flash seems odd; it could be because I was running the 32-bit version in 64-bit Ubuntu (via the flashplugin-installer package; it seemed to work fine in Jaunty *shrug*) but whatever the reason, I decided to try Adobe’s 64-bit version of Flash 10. It works well (seems a bit slower than 9, but at least it isn’t acting up) and installation is really easy!
(0) Uninstall Flash
(1) Download the .tar.gz file from the bottom of this page. (Link corrected Dec. 1)
(2) Extract the .so file (double click the .tar.gz and Archive Manager will start)
(3) Put it in the .mozilla/plugins directory of your home folder (go to your home folder, View -> Show Hidden Files, and create the plugins dir if it doesn’t already exist.
Done! Restart Firefox and test here.
Update Dec. 16: version 10.0.42.34 was released on Dec. 8