IE 8 should be able to download the manager, but you may see formatting issues with the web page as everyone is going towards html 5, which means using the latest version of javascript and css so that animations, etc. work correctly. (thats just an example)
I do recommend that you upgrade to 11, if for anything else to plug up security holes that the morons keep looking for.
There is an issue with firefox though, It maybe fixed in the latest version, When choosing any app other than the manager, you will get a error as it can not understand the file format. When choosing another app it is suppose to jump to the manager and install that instead. As the manager is required to install all the apps. So if you see the error in firefox the work around is to just choose the manager and go from there. (This paragraph is meant for anyone getting that error)