Adblock Plus is an extension for the Firefox Web browser. With Adblock Plus, users can disable and block most Internet advertisements, including pop-ups, text ads and flash advertisements. As you begin to use Adblock Plus, you'll customise the extension to block the content you want blocked. If you've set the blocking ability too high and it's blocking content you want to see, you can reset the extension and start over with a clean slate.
Start Firefox and click the "Firefox" button in the top-left corner. Mouse over "Help" to expand another menu and select "Troubleshooting Information," which will open a new tab.
Click the "Open Containing Folder" button in the "Troubleshooting Information" window. Right-click the "Adblock Plus" folder and select "Delete," confirming that you'd like to delete the folder.
Return to your Firefox browser and type "about:config" in the address bar. Upon hitting "Enter," you'll see a warning that changing advanced settings may harm Firefox's stability and that doing so voids your warranty. Firefox has no warranty; this is just a joking way for them to say that messing with these advanced settings isn't recommended unless you know what you're doing. Click "I'll be careful, I promise!" to continue.
Type "extensions.adblockplus" in the "Filter" box. Right-click each entry that appears and select "Reset" from the contextual menu. The next time you restart Firefox, Adblock Plus will be reset, as if you just installed the extension for the first time.
Refrain from altering entries in Firefox's "about:config" window if you don't know what the entry is or what altering it will do, as it may cause problems with your browser.