"It appears that your Add-on violates the Firefox Add-on Distribution Agreement and the Conditions of Use. Both prohibit Add-ons that violate the law. Your Add-on appears to be designed and promoted to allow users to circumvent paywalls, which is illegal.
...
We are responding to a specific complaint that named multiple paywall bypassing add-ons. It did not target only your add-on."
Source:
https://github.com/nextgens/anti-paywall/issues/109
"It appears that your Add-on violates the Firefox Add-on Distribution Agreement and the Conditions of Use. Both prohibit Add-ons that violate the law. Your Add-on appears to be designed and promoted to allow users to circumvent paywalls, which is illegal.
...
We are responding to a specific complaint that named multiple paywall bypassing add-ons. It did not target only your add-on."