Hello!
I have some interesting problems with my dual monitor setup on Linux Mint 16 KDE 64-bit. I have a Samsung Series 7 laptop with Intel Core i7 3630QM 2.40 GHz, AMD Radeon HD 7870 2GB, 2x4 GB DDR3.
I have 2 OS - Linux Mint 16 KDE 64-bit and WIndows 7 64-bit, side by side on a 250GB SSD. I have an external monitor LG 24'' E2441 connected via HDMI on the right side of the laptop itself and it is set as primary monitor in display settings (extended desktop).
Problems:
1. Some flash players fullscreen opens on laptop screen, but it should be always on my external monitor since it is set as primary. For example youtube.com and vimeo.com fullscreen always opens on the external screen, but all the trailers on imdb.com open the fullscreen on the laptop screen. I could give more examples, but I recon there is no need for that.
I have tried to change the graphics card driver in the driver manager, I have three options there (xserver-xorg-video-ati{recommended}, fglrx, fglrx-updates) and I tried them all without any luck, however the fglrx works better than the recommended one (I had some black fields on my screen from time to time when I open something in fullscreen)

2. Anything I open (file manager, terminal, software manager, etc.) it chooses randomly on which screen to appear, most of the time it is the screen on which i had last activity or should i say which one is focused at the moment (mouse click on the screen makes it focused) but not always. Is there any way to force to open everything on my external monitor?

3. When I watch a video exactly after 15 minutes my both screens go dark and my external monitor says HDMI Power Saving Mode and after moving the mouse you get another 15 min and so on (this thing acts randomly as well). It is not about Power Settings because I have set there to dim the screens after 10 min of inactivity and I also tried to turn that option off completely without any luck.

None of these problems occur on Windows 7.

I am new to Linux, I tried Ubuntu 12.04 and Crunchbang and now I think I am going to stick with Linux Mint KDE.
On Ubuntu I had similar problems and with Crunchbang it was a nightmare in regards dual monitor setup. With these two distros I tried different things to solve the problems but I couldn't beat it. Since now I have found a desktop environment that I like I want to configure it correctly and since with Ubuntu and Crunchbang I didn't have any luck, I decided to write this post, because it seems without help I am not going to make it. I would appreciate any advice and tips on how to solve these problems.
Thanks in advance!