We don't have a separate version of Flash Player for OS X 10.10. We are currently testing Flash Player on OS X 10.10 and once it is officially released it'll be added to the Flash Player supported browser list and you'll be able to download Flash Player from the statndard Flash Player download page at get.adobe.com/flashplayer using OS X 10.10.
For now, you can install the current version by going to get.adobe.com/flashplayer/otherversions and selecting 'Mac O S X 10.6 - 10.9' from the OS menu and then select 'Flash Player <Version Number> for Mac OS X 10.6 - 10.9'. Since we're still testing and it's not officially supported you may encounter issues. If so, feel free to file a bug at https://bugbase.adobe.com.
So will it work the same? Because my problem is, that I do have flash player installed on Yosemite, but when I go fullscreen on Youtube, I get a scaling animation I haven't seen before ever.
As I mentioned in my previous post, we are still testing Flash Player on OS X 10.10 and issues may be encountered with playback, which you have encountered. Please file a bug at https://bugbase.adobe.com and include as much information as possible on your issue, including OS version, browser, and URL to video's that exhibit the behaviour. The bug will be triaged by our QE and processed accordingly.