Navigator runs best of Firefox on PC and Chrome on Mac.
Optimize Your System for Rally Navigator - Firefox and Google Earth
Get the New Firefox with IPC Control OFF
Google Earth speed test and more info
This speed test issues a number of Google Earth plugin API calls for every frame drawn. The number of frames per second is a measure on how fast this is done.
Rally Navigator may make thousands of calls per second to the Google Earth plugin. This is called "Inter Process Communication" IPC for short. If each of those calls takes a tiny amount longer you immediately suffer massive performance penalties.
Turn off IPC Control to the Google Earth Plug In
:config" into your address bar, you'll get to a page with a lot of settings. Find the line for "dom.ipc.plugins.enabled =true" and toggle it to "false". Restart your browser and Firefox will run 3-5 times faster!
A modern computer with IPC off should be 40-60 frames per second
Hope that helps!