Question: On Ubutnu, Using firefox:   

i set it in firefox network setting(SOCKS5) when i check my ip (i.e whatsmyip.com) it is the socks server's ip, but when trying to access youtube.com it's blocked
why?!

in about:config i have set use\_remote\_socks\_dns to true, no change, set DNS server of my router to 8.8.8.8 and 8.8.4.4 , no change again, used wireshark, just got more confused...   

i know this has been asked before and it seems everyone has got their problem fixed except for me, can you please tell me what am i doing wrong?

Answer: 
I had the same issue. To fix it I changed a setting:

(Press 'alt' to view top menu then)
Tools > Options > Advanced > General (tab).

Turn off "Use hardware acceleration when available".
I ended up reinstalling Firefox after an uninstall. lorengphd's solution did not work.