>Because if all they do is take the HTML response and send it over to some web back-end with an ajax request, that looks innocent enough to any reviewer. For example, under what grounds would a reviewer flag that ajax request as malicious and prevent the extension from being published? It's not possible for them to know what purpose that data has for the extension unless they are really doing a deep dive on each review and take the extension's purpose into account based on their opinion of what it "should" do based on its description.

I think you're giving the reviewers too little credit. There's no plausible reason why you'd need to send urls to a server to perform such a trivial transformation. Also, a search of BMO[1] shows that addons are regularly being found to breach these policies and blacklisted.

[1] https://bugzilla.mozilla.org/buglist.cgi?product=Toolkit&com... control-f for "Add-ons collecting ancillary data".