Q: Can I downgrade Quicktime 10.3 on Mac OSX 10.9.5 Mavericks to play and not have to convert .mov files?

Hi, I always used to be able to open my .mov files (final exported movie from editing it Final Cut Express HD) and then use Quicktime 10.3 or maybe the previous 10 version to export it the video to play in itunes HD 1080 or HD 720, or export my video for youTube, etc.  Ever since I updated my system, Quicktime has to CONVERT all my .mov files before I am able to export them.  The preview in the finder (pressing spacebar) on .mov files also no longer works.

Is there any way to downgrade Quicktime so that this works like before, I am almost sure I had 10.9.5 on my computer before when this used to work, just that I upgraded to 10.10 some months ago, hated it, and downgraded back to 10.9.5, but Quicktime stopped working like before!

I have Handbrake 0.10.5 to export my .mov files to itunes, but I have compared the quality between the quicktime exported .m4v file and the one from Handbrake, and I feel the quality of the Quicktime version is better, but also larger in size.