How to simulate slow internet connection
Solution 1:
If you use a browser to simulate that, you can use Firefox Throttle, Internet Explorer Throttle or Fiddler.
Solution 2:
Using linux you have a software called trickle that launches a process and limits its bandwidth usage.
Solution 3:
I would check out Charles Proxy. It has bandwidth throttling and is cross-platform with a very clean interface.
Solution 4:
This is free and simple for Mac OS X and works with the every browser: speedlimit