I tried almost everything that I could find online and nothing helped.
I have a Dell Inspirion N5110, 8GB RAM, Windows 8.1 pro on a Kingston SSD drive. Graphics: Intel graphics 3000 and Nvidia GT 525M. Adobe flash player installed and up to date, as well as shockwave player. I'm using Mozilla Firefox (I tried other browsers too,
same problem, but I'm used to Mozilla and would try not changing it).
I recently reinstalled Windows. Before I had Windows 7 Ultimate on a HDD and everything worked perfectly.
Note: I had no lags whatsoever when playing any type of video on VLC player or Windows media, or when playing video games. Therefore I assume I don't have a graphics-related problem.
Graphic drivers are updated. Flash hardware acceleration is off. I tried also using Nvidia graphics for Mozilla but that didn't work. I reinstalled flash, Firefox and tried different browsers. It seems that videos in lower qualities go pretty smoothly (although it could go better), but videos on HD, mostly youtube and Vimeo are not watchable.
I hope someone can help me, I'm really frustrated not being able to use youtube and vimeo as I'm used to.
Thanks!