I installed the above add-on (from Gocomics Depaywall – Get this Extension for 🦊 Firefox (en-US)), and it worked great for several months. Now, though, the paywall comes up every time I try to access strips more than a month old. Aggravating, since (a) I want to see them, and (b) the archives used to be totally free, with no anti-paywall necessary. Please help–thanks.
I am sorry to hear that!
You could try to directly contact the developer of the add-on and share the feedback by creating an issue on their GitHub repo: https://github.com/Idiot-01/Gocomics-Depaywall