[luksol]

The issue is that XBMC on Android doesn't have direct control of your TV's refresh rate. So, while it does look like the Fire TV supports 50Hz, XBMC can't change that on the fly.

The issue is that in the UK, there's a lot more variety of content than in the US- you might want to watch a 24fps movie, followed by a 50i TV show, followed by a 25p show, followed by a 60i show. The problem stems from the fact that 30Hz-based frequencies aren't clean multiples of 25Hz-based frequencies, so not all content is going to play smoothly all the time.

In comparison, even though the US version of XBMC on Android has the same limitations (it can't change the screen sync frequency on the fly), most content is going to be in the same set of frequencies- 24,30,60 -that can all either multiply into 60, or, in the case of 24fps, use 3:2 pulldown to get there.

Ok, so if I wached some tv program on live tv via my tv (a lot of tvs ) via tv(!) tuner with 50MHz refresh rate and then switch to amazon tv (another tv! ) and watch some movie, but output is set to 60MHz, then I will have problems? Did I understood it correctly?

Only if you're watching them all from your Fire TV. If your TV can handle a 60Hz refresh rate, then you can set the Fire TV to that, and any content based on that (24Hz, 30Hz, 60Hz) should be fine. But, if you also have 50Hz-based content (25Hz, 50Hz), then that might not play nicely with the refresh rate setting you've already made.

XBMC running on Linux, Windows, or OS X can change the refresh rate setting on the fly to compensate for this. On the Fire TV, it's not possible to do so.

Thank you for your explanation.
Ok, So the problem is with the content. One of the previous posts indicates that Fire TV has the ability to switch between 50MHz and 60MHz refresh rates. Could such 'switch' be implemented in XBMC for FireTV?
Also, if I have refresh rate mismatch between my content and FireTV settings, what would outcome look like?