UPDATE : Just updated the Google Voice extension to work with Firefox Version 10. CLICK HERE to Download. Follow install instructions below.
Thanks for the emails and comments, I actually use Chrome browser more, but I have my reasons, So i'll try to stay updated with the FF versions. Details below:
This addon allows you to use your Google Voice number to call phone numbers in website pages using a click-2-call feature.
Once downloaded, open it with firefox by going to File > Open
Make sure to sign-in to your Google account by visiting settings from the extension.
You can also CLICK HERE to get the extension.