I would like to know how can I activate plugins for soundcloud.com via Tor Browser? I can't play music there and upload my tracks and photos now. Soundcloud.com is blocked in my country.
SoundCloud typically relies upon Adobe's Flash when running on desktop or laptop computers. This will not work in the Tor Browser Bundle. Flash's security problems, including information leak opportunities, are incompatible with Tor Browser's anonymity mission, so Flash is explicitly disabled.
For the future, you may wish to explore SoundCloud's recommendation for using their service without Flash. They suggest enabling GStreamer mp3 support in Firefox's about:config. This might work in a future Tor Browser Bundle release that incorporates Firefox 26 or newer if GStreamer plugins are sensible in light of Tor Browser's mission.
In the interim, you may have to consider using a VPN and a regular Firefox version in place of the Tor Browser Bundle to reach SoundCloud from your networks.
(SoundCloud's suggestion for GStreamer mp3 use is made here: http://help.soundcloud.com/customer/portal/articles/1392540-how-can-i-listen-to-soundcloud-on-linux-without-flash- )
You can torsocks together with a program like youtube-dl to download audio files from soundcloud and then play them locally.