Hi Mogens,
I would not be able to clarify all your doubts but could provide you the following information:
1. MII does not specifies any particular browser limitations. But MII screens are built on Webdynpro and Webdynpro has support for IE and Firefox thus these restrictions applies for MII also.
2. MII does not specifies any particular JRE version also. It depends totally on the Netweaver server on which MII is deployed. If the Netweaver specifies some restrictions on JRE version then it would become applicable on the applications deployed on that Netweaver server also.
Regards,
Rohit Negi.