Você pode usar o Lightspark.
Lightspark, is a free, open source Flash player. Lightspark is an LGPLv3 licensed Flash player and browser plugin written in C++/C that runs on Linux. It aims to support Adobe's newer Flash formats and AVM2 virtual machine. The last released version is 0.6.0.1, download it from here.
Lightspark currently supports YouTube well enough for daily use.1
1 Fonte: Lightspark