I got most of the answers to this question here:
Please see that thread for the details on this question.
I need some clarification on a couple of points. Will a switch between the router's HSRP link and the Pix firewalls cause any problems for HSRP? We do not have a managed switch that supports any advanced routing protocols for that part of the setup, and could someone address this concerned raised by our ISP?
"Will the default routes learned via iBGP be as attractive (different admin distances) as those learned via eBGP, if not then they may not get installed in the routing table for the purpose of load sharing. They'll provide failover, but they may not work for load sharing.
Wouldn't you have to manually load share by splitting the address space, setting up two HSRP groups on the Internet edge routers, track on the MLFR interfaces, and making each FW the failover for the other?"