when i click a link in unity documentation,it delays many seconds…responds so slow…what is wrong? and this wouldn not happen when I used unity3.5
Use Firefox or Chrome.
Wish I could give you some rep for that answer.
IE has a lot of security leaks and its libraries are (totally) outdated. Get any other browser, for your own best.
Use chrome from Google
The extansion things are awesome 
Which version IE? The online docs or local docs?