The memory consumption of Adblock Plus can be considerable in some scenarios. Firefox creates a new copy of a single stylesheet for each page being loaded (bug 988266) Memory consumption of all these copies can be very significant, like the 2 GB mentioned above for an edge case. We are working on a feature to let users send us their filter hit statistics (optional and opt-in of course) to help filter authors see which filters are actually being used and which can be removed.”]
Source: https://adblockplus.org/blog/on-the-adblock-plus-memory-consumption