This May work for you
1. Open Synaptic and looking for nsplugin and mark for completely removal
2. download Adobe Flash Player 10 from Softpedia website :
http://linux.softpedia.com/get/Internet/HTTP-WWW-/Adobe-Flash-Player-for-64-bit-Linux-42958.shtml
3. After download, extract it .. there is only have 1 file inside
4. go inside your Home folder and press CTRL+H to show "hidden files"
5. look for .firefox
6. create 1 directory thats call "plugins" (without quote)
7. copy to this "plugins" folder thats file where you was download it.
8. restart your firefox browser
good luck ...
for picture tutorial
http://news.softpedia.com/news/How-to-Install-Adobe-Flash-Player-64-bit-on-Ubuntu-8-10-98076.shtml