I can confirm this on Ubuntu 8.10 Intrepid 64bit with Flash 10. After some time Flash content will only be displayed as a grey box. Restarting the browser always works for me.
flashplugin-nonfree 10.0.15.3ubuntu1~intrepid1 firefox 3.0.5+nobinonly-0ubuntu0.8.10.1
(Linux 2.6.27-9-generic #1 SMP Thu Nov 20 22:15:32 UTC 2008 x86_64 GNU/Linux)
I can confirm this on Ubuntu 8.10 Intrepid 64bit with Flash 10. After some time Flash content will only be displayed as a grey box. Restarting the browser always works for me.
flashplugin-nonfree 10.0.15. 3ubuntu1~ intrepid1 -0ubuntu0. 8.10.1
firefox 3.0.5+nobinonly
(Linux 2.6.27-9-generic #1 SMP Thu Nov 20 22:15:32 UTC 2008 x86_64 GNU/Linux)