BTW, the second script may not work as expected if Firefox isn't currently running. In my case, anyhow, that situation results in Firefox launching but only displaying my home page.
If I modify the script thusly
tell application "Safari"
activate
set theURL to URL of document 1
end tell
tell application "Firefox" to activate
do shell script "open -a Firefox.app " & theURL
Firefox launches, opening my home page, then opens a second window to the desired URL.
