Kant 1st Imperative -- Violates -- If everyone used Adblock, many websites would shutdown. I.e. "Adblock is okay because sites can still run if just some people do it" -- cannot be universally applied, contradiction
Kant 2st Imperative -- Violates -- You treat website developers as a means to an end -- to get content, instead of rational human beings who, given a sufficient outcry against their ads, could change their ad service or offer a different model.
Utilitarianism -- Violates -- Ad Revenue - Well being of site owner: -Site Costs / Visitors + Ad Revenue For just you. Well being of you: Site benefit - time wasted * time value. (Blocking "Ad will play for x seconds" in this specific ethical system might not violate)
Rule Utilitarianism -- Violates -- Well being of site owners: Cannot make ad supported sites, current ad supported sites -site cost. Well being of society: Less websites -- more inefficiency and less units of entertainment good.
Social Contract -- Violates -- People accept ads knowing that others will do this as well and this supports the site. Another: Site owners create sites relying on users's ability to see them and thus pay for site creation.
Virtue Ethics -- Violates -- You might feel more shame being in a room with someone who made a site supported by ads and showing them that you use adblock then if you were invisible to the site owner.
The systems above are the ethical systems allowed in the book "Ethics for the Information Age (6th Edition)" by Michael J. Quinn (the list is his, but not the theories themselves, just mentioning my source to show I'm not cherry-picking ethical systems)