Adblocker that advertises to you and the developer doesn't see the irony in this and decided to cancel support after the next update because not enough people purchased something that they installed specifically to avoid paying for a service; Proving their hesitance to pay was justified due to the lack of guaranteed support in the future.

(By the way, you may want to remove that soon, because it's literally an option that's able to be selected when reporting an add-on to Mozilla: "It contains spam or inserts unwanted advertising Example: Insert ads on webpages"

The use of overlaying a payment window also isn't stated in the add-on description, it simply states that the add on "uses extensionpay.com as a payment processor integrated with Stripe for obtaining a one-time lifetime license after an initial free trial period", no where does this state that the add-on will be overlaying this by force; this violates the "No surprises" Mozilla Add-on Policy which specifies "Users should be able to easily discern what the functionality of your add-on is and should not be presented with unexpected user experiences after installing it." )