Apparently if you try to run a completely off the public Internet install of Cisco FMC, things doesn't really run properly as the menu Javascript libraries are hosted on a Google server. Therefore you cannot navigate thru the system, rendering the FMC useless.
A pretty simple PoC can be done by adding a null entry to www.googletagmanager.com into your hosts file or DNS RPZ.
Any chance Cisco could pretend they too are a security company and not rely on third party products, in particular on their security ones? Apologies if this sounds as a rant, but if you have to rely on a third party company to run your products and solutions, you better off get your tools from this third party and take Cisco out of the equation.