The variable firefox is not defined

I know that there must be a really simple solution to this that i’m overlooking, but i’m using the script below and receiving an error stating ““The variable firefox is not defined.” number -2753 from “firefox””. What am i missing?

tell application firefox
	if it is running then
		get URL "http://..."
	end if
end tell

AppleScript: 2.1.1
Browser: Firefox 3.5.5
Operating System: Mac OS X (10.6)

The double quotes

it seems i messed up the quotes a bit in my original message. i didn’t have them at all in my script. so that’s solved now. thanks.