How to block Facebook ads within the Firefox browser:
1. Go to this page:
https://addons.mozilla.org/en-US/firefox/addon/1865
2. Click: Add To Firefox
3. Wait for Install button to become active then click it.
4. Restart Firefox.
5. When Firefox opens, you should see a tab: Add Adblock Plus Filter subscription
6. If you want to block ads on many other sites, click the button next to EasyList (USA), then click Subscribe.
7. Under the Tools menu in Firefox, select Adblock Plus Preferences.
8. Click the Add Filter button.
9. Copy and paste the following filter: facebook.com#*(social_ad) and click OK.
10. Repeat steps 7 and 8, then copy and paste the following filter: facebook.com#*(social_ad_advert) and click OK.
11. Close Firefox, then open it and go to Facebook. Adblock Plus should block all Facebook ads.