Flash on Linux was discontinued in 2012: http://www.pcworld.com/article/250784/for_flash_on_linux_the...

Even back then you had to do hacks to get it to work. But after that it became very hard to get anything to work. Eventually someone came out with a service called pipelight that I used to use that would allow you to use windows only plugins in Firefox: https://wiki.archlinux.org/index.php/Pipelight. It worked great until I didn't need it anymore.