ShowIP seems to work as well as ever.
After install and Firefox' restart, ShowIP politely asked to install the AdBeaver adware. I declined, I see no sign of adware, and ShowIP works fine.
I have no objection to the developers seeking payment for their hard work, as long as they do it openly and honestly. If you don't want to use the adware, consider donating.
To the devs: If you could monetize it without impacting my privacy, I'd do it. Perhaps at least include a link to donations in the window asking about AdBeaver.