Yes, you have to download the full version everytime you upgrade, but its only about 6 megs for the win32 build and it's well wroth it.
One night with firebird has gave me a better browsing experance then years and years with IE and others. Trust me, try it and most likely you will fall in love.
also, read this before trying to install any plug-in's:
http://texturizer.net/firebird/edit.html