Is an upgrade to a modern OS out of the question?
my concern is i will lose all my settings, progs, files etc doing an upgrade - is this the case?
Firefox. It will ask if you want to import from Chrome as soon as you install it.
Not if you install from within the OS as far as I am aware. If you go the upgrade path, it makes a folder with all your old stuff in so you don't lose anything.
If you do fresh install then yeah, you'll lose stuff!
You really should have a back up of all your stuff anyway, hard drive could go anytime.
Settings are usually pretty minimal, not saying a new OS won't be different but don't normally have to change to much.
Firefox. It will ask if you want to import from Chrome as soon as you install it.
^ This.
Assuming your Vista install in 64-bit, then grab yourself the 64-bit Firefox beta as it seems to work really well and personally has performed better for me than then normal 32-bit client.
On a side note if the Vista install isn't 64-bit then an inplace upgrade to a newer OS won't be possible. You'd have to format and install fresh.
Please note that 64-bit builds of Firefox are only supported on Windows 7 and higher.