Hi there!

Thanks for reaching out to us! We are aware that most add-ons on Firefox  including Adblock Plus were deactivated due to an issue with the browser’s signing certificate expiring. Mozilla has released an official update to deal with this issue https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/.  If the update has not yet reached you, please try updating manually using this link https://www.mozilla.org/en-US/firefox/new/. Let us know if this resolves your issue! Reach out to us via support@adblockplus.org if you are still having this issue.

Thanks
Shannon
ABP Support Team