Green Screen - Firefox - 11.5.502 + video distortion

Hello, I have two issues with video playback.

1# With hardware acceleration on, I get green screen with sound on any flash video. For example http://www.youtube.com/watch?v=JMqzgo1Sd2I&hd=1

Disabling HW acceleration works for me, but I would like to keep it enabled. I describe why in my second issue.

I went through the other topics about this issue and I've tried stuff:

Antivirus - I have AVG, temporarily unstalling had no effect.

Windows updates - I read about two updates labelled KB27something in the other topic here, but I do not have them installed at all.

MXMSL 4.0 SP3 parser - in one older topic someone fixed it by updating this stuff, I did that, it didn't help either.

My computer should be this one http://www.sony.co.uk/support/en/product/SVE14A1S1EP/updates, but the drivers listed there are from 4/2012, kinda outdated, so I downloaded newest drivers I could find from Intel and AMD sites respectively.

I have switchable graphics setup:

1) Intel HD Graphics 3000, i'm using driver version 9.17.10.2932 from December 2012, according to the Intel website this is the latest.

2) AMD Radeon HD 7570/7670M [Sony], i'm using driver version 9.10.8.0 from October 2012, I couldn't find this driver standalone at AMD website.

And I can choose which app will use which graphics card, it doesn't matter if I run the notebook from battery or power.

I'm permanently running on Windows 7 "High Performance" preset, which should disable any limiters/power saving.

Any ideas?

2# I'd like to keep the HW acceleration enabled, because when I watch a 720p or lower resolution video on my 1680x1050 screen in fullscreen mode with HW acceleration disabled, it causes the video to become distorted and generates some minor artifacts that destroy the high quality feeling of the vid. It only happens with HW acceleration disabled, and only when watching a video. When I watch a high quality livestream with maximum resolution of 720p, the livestream is fine. Also, when I watch any video at 1080p resolution, the problem disappears. It happens at different websites, for example youtube, twitch.tv. Changing my screen resolution to lower setting does not help.

It's not a problem of the video either, because even the overlay texts/icons of the web player become distorted. But it only happens with videos on the websites, so I suspect Flash player. When I download the video and run it fullscreen from my HDD, it looks fine. See examples:

http://dl.dropbox.com/u/48388389/web_player.png - youtube at 720p, fullscreen mode

http://dl.dropbox.com/u/48388389/vlc_player.png - same video downloaded, using VLC player, fullscreen mode

Seems to me that the flash player has some issues with stretching video without the HW acceleration enabled.

I have no problem running videos with HW acceleration off as long as I can fix the 2# issue, so either one of these will do for me

Thank you for your help.