So here's how I fixed it. Well, got Adblock installed on Firefox.
1. Open up your old crusty, never used version of Internet Explorer that's on the desktop. I'm using Windows XP which has it installed by default. If you have an updated version of Internet Explorer then I'm pretty sure that will work fine also.
2. Go to the Adblock website using Internet Explorer: https://adblockplus.org/en/firefox
3. Click the "Install for Firefox" button and it will open a downloadable file
4. Save the file to your desktop
5. Go to the desktop and double click the file
It will say windows can't open this file because it's an unknown file type.
6. Choose "Select Program from a list". Press OK.
7. Choose Firefox from the list
You should now have an Install Add-ons Firefox box on your screen. Click Adblock Plus and press install now.
And that's it. You should now have Adblock Plus installed on Firefox. Hope this helped you out.
Update: You can now get Adblock installed on your mobile devices. No more annoying ads on your Smartphone! Compatible with Android and iOS devices. Check out the link for more information and to download: Adblock For Mobile.