The App, a one-click icon I keep on my desktop that opens the full version of Google Maps in FireFox, is written entirely in Applescript. Find the native Applescript Editor inside the Utilities folder inside your Applications folder. Open it.
Here's a link to a web page with details on how to write the code:
http://stackoverflow.com/questions/3645763/how-do-i-instruct-applescript-to-open -a-new-firefox-window-with-a-link
My code ended up looking like this:
tell application "Firefox" to activate
tell application "Firefox"
open location "https://www.google.com/maps/"
end tell
After you've successfully run and/or compiled the code, save your work as an Application. Mine sits on the desktop and looks like this. I substituted a custom icon for the default Applescript Icon so it's a little easier to spot on the desktop.
One small thing about this code... if Firefox is not already open -- when it opens, it opens a blank page and then opens an additional page to load Firefox so you end up with two Firefox windows instead of one. Not a big deal. The extra window sits beneath the active Google Map and doesn't impede workflow. It's just an extra window to close when you're done with Firefox. There's probably a way to write this script such that you'll only get one window when you activate Firefox and load Google Maps but the extra window was not enough of an annoyance for me to sort it out. This code was tested in OS X 10.7.5 and works great.
_________________________________
The Service, written for Safari, enabling you to open your current Safari page/URL, in Firefox, is actually written using Automator (native). Find Automator inside your Applications folder, open it, and select "Service" from the icon options and drag "Run Shell Script" from the list of actions, into the Automator workflow area. Here's a link to a page with detailed instructions.
https://discussions.apple.com/thread/6624316?start=0&tstart=0
Follow them exactly as explained in the post by Hiroto -- careful to make sure you execute all the instructions in both step 0 and step 1. If you duplicate his settings in "Run Shell Script", it should work perfectly. Again, I've tested this service in OS X 10.7.5 with Safari 6.1.6 and it works every time. The only catch is that the Safari active webpage URL must be highlighted entirely in order for the Service to show up in the Services Menu. (click URL field + command A). This is what the Safari Service looks like when it's done. When I saved it in Automator, I named it "Open Safari URL in Firefox".