As noted above you should get rid of swfdec and gnash (if you have it).
Two other suggestions you could try if the above does not work.
1 - Try installing swiftfox and see if it performs better.
2 - There is a beta version of the newest Adobe that I have had much success with. I only reccomend this as a last option as you will be installing something directly. Being that it has no repo there will be no updates automatically and you would have to update it yourself.
(I suggest this because my wife had issue with Bejeweled on Facebook. This version of Flash cleared it up for her)
I have only tested these instructions in Firefox/Swiftfox. I do not know if they work outside of that.
- Remove all flash plugins via your preferred package manager
- Close Firefox/Swiftfox
- Open a terminal and type the following
This removes the file for the flash plugin incase the uninstall does not do it.
sudo rm /usr/lib/mozilla/plugins/libflashplayer.so
- Download the following
This is the 10.1rc2 release
- Extract the libflashplayer.so to your home folder
- type the following in the terminal
Restart you favorite "fox" type browser and type aboutlugins to see if everything worked.
sudo cp libflashplayer.so /usr/lib/mozilla/plugins/
Please note that if you decide to do this, then go back to the repositories you should hand delete the file using the rm line before starting.
Use at your own risk...yadda yadda