You don't even need applescript.
In Safari's Preferences, go to the Advanced tab and check "Show Develop menu in menubar"
Then when you're on a web page, go to Develop -> Open Page With -> Firefox
...and any other browser you may have installed.
Many thanks for that, Kevin.
I've got no idea why, but your method surpasses the AppleScript method in that it takes me to a more pertinent page.
By way of example, if I use the AppleScript I created (dk's second suggestion) on this page I'm taken to an FTM log-in page, whereas if I use the "Develop" method I'm taken to this page, although (obviously) not as a logged-in user. Similarly, the different methods take me to different "start" pages on the Staples Web site.
