Websites in Ubuntu take a very long time to load. In Windows, it all works fine. The download speed is normal.
Here's a video capture to show what I mean.
That looks like you have a broken non-responding DNS server listed first in your network config. Check in
Your ISP should give you DNS server entries which are in their own network and will be pretty fast for you - make sure you're using those; although given the speed it's currently working at, any working DNS server will probably be better :)
Windows make an heavy use of the cache when Ubuntu does not.
Probably you only need faster DNS or you can setup bind9 as "caching server" https://help.ubuntu.com/community/BIND9ServerHowto and on the internet is plenty of lists of free public DNS servers http://www.google.com/search?q=public+dns