The adblock community maintains a number of different "block lists" of domains and resources that should be blocked from loading. One particular list (Easylist) is used by the most popular extensions AdblockPlus and Adblock. This list does not block PageFair's analytics from loading. There is an additional list called EasyPrivacy which is not used by default in AdblockPlus or Adblock, but is used by default in uBlock. Our analytics (as well as most other analytics tools like Google Analytics) are blocked by the EasyPrivacy list.
You should be able to try out a different extension to verify this.