Updating to F7: how does the installer know where put an app?

[Michael Klinosky]

When I put F7 on my primary machine, I want to upgrade (not 'new 
install') so I don't have to recreate my system.

But, I'm concerned about one of my applications (Firefox). The reason 
for my concern: Recall, from a few months ago, that I upgraded my FC6 
install of Firefox 1.5 to ver 2, _and_ put it into /usr/local.

Will the installer look at that, and put the new Firefox there? Or, will 
it not care, and put it in its default location?

If the former, what did I have to do to tell it to use the one in 
/usr/local?