It's updating the thumbnail screenshots. This only happens if you have the Safari "blank page" be your favorites instead of either your "home page" or a truly blank page.

Literally the reason HTTP verbs are a thing is so that User Agents like Safari can do exactly this. If this weren't a by-design property of the HTTP protocol, we wouldn't even have methods. Read the spec!

If I recall, Safari's default is to show your "favourites" screen in a new tab, which routinely refetches to update icons/previews.

I'm skeptical that it's "every time" but I do remember it doing it way more than I thought was needed.

Now I wonder if Safari (& other browsers) has distinct headers for their favorites lookups, to tell these lookups apart from real users and discard these accesses from site analytics..

Hey! I've been thinking about this all day. I thought it was a GET to fetch the title of the page, but it might only be an OPTIONS or HEAD request? I'm not sure. Either way, my code activates the garage door on that endpoint no matter the HTTP verb.