cbox is not working in firefox. saying that its blocked - The resource at “https://www5.cbox.ws/box/?boxid=...” was blocked because Enhanced Tracking Protection is enabled.

I use atabook,,, it should work on your site. You can also have the link lead to atabook itself, not sure how to explain what I mean. There are other guestbooks though. I suggest looking through Reddit to see which one you think would work for you.