The 64 Kernel can be a buggy and you may better off installing the 32 bit
version of Ubutun. Or yet, you may need to install the 32 bit version of FF for
the AMD.

https://wiki.ubuntu.com/32bitBrowserOnAmd64?highlight=%28AMD%29
https://help.ubuntu.com/community/AMD64/FirefoxAndPlugins?action=show&redirect=F\
irefoxAMD64FlashJava