Hi there,
Mozilla is having a widespread issue with nearly ALL add-ons due to a Firefox issue.
They've already deployed a fix for it, which should be installed for you soon: https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/

If this issue still exists past Sunday, please reach out to us via support@adblockplus.org!
Thanks,
Jessy
ABP Support Team