You might have noticed in your most recent update of Facebook there's a little paper plane icon in the top left corner. That's the new Firefox share button. It allows you to share to a number of social media accounts with no addons necessary. It's also easy to set up.
As long as you are already logged in to the account(s) you'd like to add, you can do it with a single click. simply go to the Activations webpage then scroll down and choose which accounts you'd like to include. You can change/delete these options later by going to the Add-ons manager and clicking on 'Services'.