Laggy video streaming in Safari

Hi all.

I've recently had a problem with the hard drive on my MBP 13" (mid-2010), which forced me to change it. I used the occasion to freshen up my Mac by installing an SSD and by doubling up its RAM (from 4 to 8GB).

At the reboot, I also installed Yosemite (i was on Mavericks before the hard drive problem).

Everything seems fine now, the SSD is mostly empty and the RAM is twice the size now, so everything's very fast of course.

The problem I'm noticing, though, it's that video streaming is often a bit laggy on Safari. It's not a slow connection problem, as the buffering goes on, as well as sound, only the video freezes out for a while every few seconds. The strange thing is that this issue doesn't occur in Chrome, where streaming is perfectly smooth.

The only thing I came up with was reinstalling Flash Player, which I did with no effects. Any ideas? Having changed so much simultaneously (both hardware and operative system) I don't know which way to look at.

Thank you in advance!