Blocking HTTP content when connecting to HTTPS sites allows Firefox to establish a full secured connection to those sites, which aids against snooping attacks. Of course, I know that many sites suffer usability issues if HTTP content is blocked, due to drawing content from unsecured connections, but this blocking could also be used to block advertisers on SSL-secured sites. Most average users (I think) expect HTTPS to be secure, but some sites draw their advertisements or tracking scripts from HTTP connections, even though their own content is supposedly encrypted; as you just said, Firefox sees all the content as lacking protection, so users wouldn't know that their information could still be compromised. Regardless, adding protocol restriction to ABP just increases usability, since someone may want to block all images only on HTTPS domains, or all objects on HTTP, etc. I am sure that people would find more uses for it if it were added, than I can think of. Like Anti-Ad said, a subscription list for this could potentially improve general internet security. Thanks for reading! Please let me know if anything I said isn't true (I'm still learning).