You might have heard of the Adblock extension that has a massive list of URL filters to block out adverts from most websites. Does this slow down Firefox, considering that for every little image and flash it has to consult that massive URL whitelist?
Firefox – Does Adblock slow down Firefox
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Best Answer
Most of the blocked content is made up of flash files, images and scripts. These are quite large and require time to download.
So, by blocking them Adblock actually improves the loading time, sometimes by a lot.