Firefox: Ad blockers are 2021’s most popular browser extensions

Multiple ad blockers topped Firefox’s list of the most popular and innovative add-on browser extensions of 2021. 

Firefox determines which add-ons are “most popular” by calculating their average daily users (ADU) throughout the entire year. Adblock Plus averaged 6,134,231 daily users while uBlock Origin averaged 5,011,974 throughout 2021. Firefox notes that uBlock Origin is hot on Adblock Plus’ heels, closing the gap between the two as the year progressed. Firefox estimates that the add-on may pass Adblock Plus at some point in 2022. 

Privacy appears to be a significant issue for Firefox users. Other top extensions in 2021 include Mozilla’s Facebook Container (1,740,395 ADU) and tracking add-on Ghostery (1,167,938 ADU). 



Firefox data shows that of the 133 million visits to in 2021, most came from people based in China and the US. Germany, France, and Russia filled out the rest of the top five. Firefox also says that 60% of Russian users have installed an add-on, far surpassing the percentage for any other region. 

One-third of all users have installed an add-on, says Firefox, and there were 127 million total Firefox add-on installs in 2021 alone. 

Firefox also highlighted several extensions that met Mozilla’s “standards of security, utility, and user experience.” The list includes tab organizer add-ons like Sidebery and Tab Stash as well as website design tools like Stylebot and automaticDark.

In October, Mozilla’s Firefox browser team cracked down on malicious add-ons. The team blocked ones that were misusing the browser’s proxy API, which software uses to manage how the browser connects to the internet.

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