uBlock Origin and Adblock Plus are the most popular extensions on Firefox, with each around 5 to 5.5 million average daily users over a whole year[1].

I believe the addon page is average daily users over a week or 6 days?[2]

Firefox monthly active users (unique over 28 days) is around 200 to 210 million worldwide (26 to 22 million in the USA)[3].

It's probably wrong to compare those numbers but a very naive 200 / 28 = 7.41 million average unique users per day. 5 / 7.41 = 67% (probably wrong)

[1] https://addons.mozilla.org/blog/firefoxs-most-popular-innova...

[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1168642

[3] https://data.firefox.com/dashboard/user-activity