About this Add-on
Visit the webpage you want to share then Click on the add-on's button on the toolbar.
It works just like the Google+ Share buttons you can find on the websites.
The bonus is that, this add-on can let you share posts as your Google+ Pages instead of your profile.
After installing the add-on, If you can not find the add-on button on the browsers toolbar. Enter Firefox's customization screen by Menu >> Customize or Right click on the toolbar and select Customize.
The you can find the add-on's button on the Browser Pallet. Just drag and drop the button where ever you want.