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Open Firefox. Open the Adblock Plus extension page. Click + Add to Firefox. Click Add when prompted. Close the Adblock Plus tab when it opens. Watch YouTube videos without ads.
Click or double-click the Firefox app icon, which resembles an orange fox on a blue sphere. This is the official Firefox page for Adblock Plus. It's on the right side of the page. Doing so adds Adblock Plus to your Firefox browser. Once this tab opens, Adblock Plus has been successfully installed. Now that Adblock Plus is installed, YouTube videos will no longer display ads.