Report Manager vs. Report Server

I have reports in report manager that will not render in browsers that are outside of the supported list for 2008(as expected) but they will render via report server. Why is that? I'm not understanding the difference in the interaction with the browsers across the two methods.

Any insight will be greatly appreciated!

Check to make sure JavaScript is enabled in the browser. I still had some trouble so I installed IE tab for Chrome.

Here is some additional information on non-IE SSRS browser support: