Online videos load extremely slow (firefox 18)

I have high speed cable internet and a gaming PC I built (Gigabyte Z77Xud3H; Gigabyte GTX 660; i5-3570K; 250gb Velociraptor @ 10000rpm; 2x4 GB ram).

I use Firefox 18.

But when I want to watch any type of video on any website (youtube, vimeo, IMDB, or any website what so ever that has videos), the videos take long to load, or I get the looping circle thing going round without the video loading.

I usually go to settings on the video it self and set local storage to "unlimited". All my drivers are updated.
I checked with my internet provider and they tested my speed and connection and it is exactly as advertised. I tested it with speedtest.net too.

So I can't find out why in the world videos take long to load. Any ideas?