I had no idea about this so just making a post.
Obviously flash hasnt been updated for linux in forever, version 11.2? current windows version is like 17 or something. However the flash in google chrome is still maintained
Anyway you can use a plugin called freshplugin to get the latest chrome pepperflash to work with firefox.
Just a simple yaourt -S freshbrowserplugin for me and suddenly firefox has flash v. 17 working flawlessly.