> for private reasons (nvtv support in fact ;) I'm running NetBSD/i386 on
> my Shuttle SN85G4v3. I've just tested WinXP-64 on it and have issues
> (which we don't care here ;) too.

tested too - actually slower than WinXP/i386 ;)

>
> I read that even Solaris runs apps in 32bit-mode (firefox) on sparc64.
> This makes me believe, firefox is not written 64bits in mind.

no idea why, i'm running firefox on my amd64 as 64-bit app. works fine and 
fast.

> So, even if I compile/run firefox (from pkgsrc) on NetBSD/amd64, I
> guess it's not using all the benefits of amd64 specifics arch, true ?

actually in NetBSD/amd64 there are some problems running 32-bit 
non-native apps, like 64-bit only linux emulation.

all native apps are 64-bit.

>
> My question is, when you have to run NetBSD/i386 on an AMD64 machine
> (for driver or app support), to what extend do you get the benefits
> from the AMD64 architecture ?
>
you will have exactly the same driver support on NetBSD/i386 and 
NetBSD/amd64 because NetBSD is really designed to be cross-platform.

in sources - the only real difference is small part of kernel code.